How do I restart a do-while loop if the last condition fails?

I've tried this myself and have looked everywhere for an answer and can't seem to find a suitable workaround. I've found many answers on this site before so I've signed up to ask my question. I have a program that loops through 6 users and assign them to a position. Users: Alpha, bravo, charlie, delta, echo and frank. Positions: 1,2,3,4,5,6. I'm generating random numbers to assign the user to their position. I have one rule that I am checking for; no user can be assigned to the same position twice. Because of this rule and the random assignment of the users to stations, sometimes the only user left for position 6 is a user that has already been assigned to position 6 in a previous rotation. When this happens my program crashes and rightfully so. How do I overcome this? I've had instances where the program will make the right choices and I have 6 successful rotations. I would like to have 6 successful rotations every time. I have spent two week trying to figure this out. Any help I can get would be greatly appreciated. Thank you. I've pasted my code below. I'm using Java.

import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.border.EmptyBorder;
import java.awt.Color;
import java.awt.CardLayout;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
import javax.swing.JButton;


public class test extends JFrame implements ActionListener {

    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private JPanel contentPane;

    /**
     * Launch the application.
     */
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                try {
                    test frame = new test();
                    frame.setVisible(true);
                } catch (Exception e) {
                    e.printStackTrace();
                }
            }
        });
    }

    /**
     * Create the frame.
     */



    //TODO  
    int randnum[] = new int [7];
    int numOfRotations = 1;
    String[] String_CurrentOperator = new String[7];
    Random rand_opers = new Random();

    List<Integer> ArrayList_UsedRandNums = new ArrayList<>();
    List<List<String>> ArrayList_MainOperatorHistory = new ArrayList<List<String>>();
    List<String> ArrayList_AllOpers = new ArrayList<>();
    List<String> ArrayList_UsedOpers = new ArrayList<>();
    List<String> ArrayList_OperatorHistory1 = new ArrayList<>(); 
    List<String> ArrayList_OperatorHistory2 = new ArrayList<>(); 
    List<String> ArrayList_OperatorHistory3 = new ArrayList<>(); 
    List<String> ArrayList_OperatorHistory4 = new ArrayList<>(); 
    List<String> ArrayList_OperatorHistory5 = new ArrayList<>(); 
    List<String> ArrayList_OperatorHistory6 = new ArrayList<>(); 


    public test() {
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setBounds(100, 100, 450, 300);
        contentPane = new JPanel();
        contentPane.setBackground(Color.DARK_GRAY);
        contentPane.setBorder(new EmptyBorder(5, 5, 5, 5));
        setContentPane(contentPane);
        contentPane.setLayout(new CardLayout(0, 0));

        JButton btnShuffle = new JButton("SHUFFLE");
        contentPane.add(btnShuffle, "name_253561263644851");
        btnShuffle.addActionListener(this);

        ArrayList_AllOpers.add("POSITION ZERO");
        ArrayList_AllOpers.add("Alpha");
        ArrayList_AllOpers.add("Bravo");
        ArrayList_AllOpers.add("Charlie");
        ArrayList_AllOpers.add("Delta");
        ArrayList_AllOpers.add("Echo");
        ArrayList_AllOpers.add("Frank");

        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory1);
        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory1);
        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory2);
        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory3);
        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory4);
        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory5);
        ArrayList_MainOperatorHistory.add(ArrayList_OperatorHistory6);
    }


    public void actionPerformed(ActionEvent arg0) {

        /*******************************
         *****ASSIGN ALL OPERATORS******
         *******************************/
        System.out.println("THIS IS ROTATION "+numOfRotations);
        genRandoms();

        for(int i=1; i<6+1; i++){
            do{
                //randnum[i] = rand_opers.nextInt(6)+1;
                String_CurrentOperator[i] = ArrayList_AllOpers.get(randnum[i]);
            }
            while(ArrayList_UsedOpers.contains(String_CurrentOperator[i]) || ArrayList_MainOperatorHistory.get(i).contains(String_CurrentOperator[i]));

            ArrayList_UsedOpers.add(String_CurrentOperator[i]); //add to used names thus far
        }


        for(int i=1; i<6+1; i++){
            System.out.println(String_CurrentOperator[i]);                       //Prints the name of the operator working on the station               
            ArrayList_MainOperatorHistory.get(i).add(String_CurrentOperator[i]); //adds operator to list of all users who have been assigned to this station
        }

        //Perform cleanup actions for next iteration of the loop
        numOfRotations++;               //increment the rotation count by 1
        ArrayList_UsedRandNums.clear(); //clear the list of randum numbers used
        ArrayList_UsedOpers.clear();    //clear the list of assigned operators
        System.out.println("");
    }   


    public void genRandoms(){
        for(int i=1; i<6+1; i++){
            do{
                randnum[i] = rand_opers.nextInt(6)+1;
            }
            while (ArrayList_UsedRandNums.contains(randnum[i]));

            ArrayList_UsedRandNums.add(randnum[i]);   //add randnum[i] to list of random numbers used thus far
        }
    }
}