How to Add multithreading to a checker

[69]

i have just create a basic checker and i want add multithreading . i used tasks but no boost performance the same cpm what should i use and how ? 
this is the part of code i want use threads on 
 

Code:

 
for (int i= backint-1; i < passwordlist.Count;i++)
            {
                if (!tokenSource.IsCancellationRequested)//basically if you didnt find password do dis . i add it to exit the for loop
                {
                    double nisba = (Convert.ToDouble(Attemps) / Convert.ToDouble(passwordlist.Count)) * 100;
                    Console.Write("\r{0:0.000}%", nisba);
                    Check(passwordlist[i], tokenSource);

                    Attemps++;

                    SaveAttemps(Attemps);
                }

[452]

Dm me - Vexisz#1337

“No one cared who I was until I put on a mask.” – Obito Uchiha

[9]

new Thread(() => { }).Start()

[330]

Code:

 
for (int i = 1; i <= threads; i++)
{
    while (passwordlist.Count > i)
    {
         Check();
    }
}


public static void Check()
{
                      if (!tokenSource.IsCancellationRequested)//basically if you didnt find password do dis . i add it to exit the for loop
                {
                    double nisba = (Convert.ToDouble(Attemps) / Convert.ToDouble(passwordlist.Count)) * 100;
                    Console.Write("\r{0:0.000}%", nisba);
                    Check(passwordlist[i], tokenSource);

                    Attemps++;

                    SaveAttemps(Attemps);
                }
}

Not sure that works 100% because i dont have source to verify ofc.