c# delete previous random generated string

I have a program where it randomly generates a new password and then writes it on a text file.

The issue is that when I try to generate a new password, it writes the new password plus the previously generated password.

I want to just write down the newly generated password, excluding the previous one

This is the code for the string password:

        string password = "";
        string pathUserPass = @"C:\Users\Name\Desktop\test\UserPass.txt";
        string pathXD = @"C:\Users\Name\Desktop\test";
        var fileUserPass = new FileInfo(pathUserPass);
        string Response;

        int r, k;
        Random Rand = new Random();
        for (int i = 0; i < 10; i++)
        {
            r = Rand.Next(3);
            if (r == 0)
            {
                k = Rand.Next(0, 25);
                password += charPassword[k];
            }

            else if (r == 1)
            {
                k = Rand.Next(0, 25);
                password += charPassword[k];
            }

            else if (r == 2)
            {
                k = Rand.Next(0, 9);
                password += charPassword[k];
            }
        }

This is my code that writes a newly generated password:

        else if (File.Exists(pathUserPass) && fileUserPass.Length > 0)
        {
            while(true)
            {
                try
                {
                    using (var tw = new StreamWriter(pathUserPass, true))
                    {
                        while (password == password)
                        {
                            for (int i = 0; i < 10; i++)
                            {
                                r = Rand.Next(3);
                                if (r == 0)
                                {
                                    k = Rand.Next(0, 25);
                                    password += charPassword[k];
                                }

                                else if (r == 1)
                                {
                                    k = Rand.Next(0, 25);
                                    password += charPassword[k];
                                }

                                else if (r == 2)
                                {
                                    k = Rand.Next(0, 9);
                                    password += charPassword[k];
                                }
                            }
                            tw.WriteLine(password);
                            Console.WriteLine("Wrote {0}", password);
                        }
                    }
                    Console.Read();
                }
                catch (UnauthorizedAccessException e)
                {
                    Console.WriteLine(e);
                    Console.Read();
                }
                catch (IOException e)
                {
                    Console.WriteLine(e);
                    Console.Read();
                }
            }

OutPut:

awbicsoatfibutdbqgrf

awbicsoatfibutdbqgrfkabeokksnd

awbicsoatfibutdbqgrfkabeokksndedmmscajpd

awbicsoatfibutdbqgrfkabeokksndedmmscajpdjdcqsepbcg

awbicsoatfibutdbqgrfkabeokksndedmmscajpdjdcqsepbcgyidlctlcpk

awbicsoatfibutdbqgrfkabeokksndedmmscajpdjdcqsepbcgyidlctlcpkiidjfcbiih

awbicsoatfibutdbqgrfkabeokksndedmmscajpdjdcqsepbcgyidlctlcpkiidjfcbiihbccqhuxpgg

Any ideas of taking out the previous generated string? I appreciate anyone reading this. Thx :)