Failing at creating modular Random Number Generator utilizing Mersenne Twister

This code works alright if I just have it as is , in main. I can take out the method call to do_something() and just do a cout and it performs as expected. I desire to build it into a modular randomizer method and failing. Can someone correct me so that I am correctly calling the mersenne twister, or even a simpler way to implement a modular rand function ? I know I've overdone the libraries in the h file. Thank you.

randomizer.h:

'''

  #include <iostream>
        #ifndef RAND_H_
        #define RAND_H_
        #include <random>
        #include <string>
        #include <vector>
        #include <functional>
        using namespace std;
        
        class Randomizer {    
        public:   
            gen();
            void do_something() {}   
        };
        #endif

'''

randomizer.cpp:

'''

 #include <random>
    #include <iostream>
    #include "randomizer.h"
    using namespace std;
    
    int main()
    {
        random_device rd;   // non-deterministic generator
          // to seed mersenne twister.
                            // replace the call to rd() with a
                            // constant value to get repeatable
        Randomizer m;
        m.do_something();
        
    }

'''

main.cpp

'''

#include <random>
#include <iostream>
#include "randomizer.h"
using namespace std;

    int main()
    {
        random_device rd;   // non-deterministic generator
          // to seed mersenne twister.
                            // replace the call to rd() with a
        mt19937 gen(rd());                    // constant value to get repeatable
        Randomizer m;
        m.do_something();
        
    }

'''