"how do i check this value in the password"

You must fail, if you view your task as an complete monolithic chunk.

You must also fail if you look on any example as an whole monolithic chunk.

Please get a sheet of paper and divide your task in many small and easy subtasks.
Divide it how often it was needed until you understand, how you can do it.

E.g.:

start:
-> scanning key matrix
-> debounce
-> check if key changed from released to the pressed state
-> convert key code to number
-> store number in RAM
... and so on.


Peter