...
...
string[] doctors = File.ReadAllLines("Doctor.csv");
    for (int i = 1; i < doctors.Length; i++)
      {
       string[] doctors2 = doctors[i].Split(',');
       if (doctorID == doctors2[0])
          { 
            //Not sure what to do here to replace values
          }

       }

...
...
string[] doctors = File.ReadAllLines("Doctor.csv");
    for (int i = 1; i < doctors.Length; i++)
      {
       string[] doctors2 = doctors[i].Split(',');
       if (doctorID == doctors2[0])
          { 
            //Not sure what to do here to replace values
          }

       }

for (int i = 1; i < 13; i++)   
    Console.WriteLine("{0,-1} {1,8}", i, numUser * i);

for (int i = 1; i < 13; i++)   
    Console.WriteLine("{0,-1} {1,8}", i, numUser * i);