I've used Android Studio's app-sign to sign my App, and configed build process automatically sign my apk. But I forget my key, and when my build my app, I get such exception,
Error:Execution failed for task ':app:packageDebug'. Failed to read
key xxApp from store "C:\Users\^-^\Desktop\app.jks": Keystore was
tampered with, or password was incorrect
You can always re-sign an app with a different (new) key, however with a different key you won't be able to upload updates to Play Store and even update the app directly on the device with such APK. The same key must be used throughout the lifetime of the application in the OS and Store, otherwise it won't be recognized as 'the same application`, so in this sense, if you forgot the password to your key, there is practically nothing you can do about it.