I’m experienced with C# already so my solution deviated a little bit from what has been taught so far in the content of the course.
I created the member variable “string password” but I also created a new method called SetPassword() which is called within StartGame().
SetPassword() uses a switch to check the value of “level” and assign the appropriate string value to the “password” member variable.
I also added another else-if block to the “OnUserInput” that checks if the currentScreen == Screen.Password.
If it does, it calls CheckPassword(input) which uses an if-else statement to determine if the input matched the password or not and gives the proper output to the user (similar to what was shown in the lesson). 
Working out pretty good so far!