forgot passcode for apple AirPort time capsule

Perform a Soft Reset on the AirPort Time Capsule to reset the password that you need. This Apple Support document will tell you how.

https://support.apple.com/en-us/HT201945

Not sure why, but for some reason users sometimes seem to have trouble with this. If that might be the case, you will need to perform a Hard Reset and then set up the AirPort Time Capsule again, just like you did when you set it up for the first time.

Note......a Hard Reset will not affect any of the stored data on the AirPort Time Capsule hard drive......only the network settings are affected.