How to restore/recover accidentally deleted key from google Authenticator?
By deletion of key, if you mean to say that you've deleted your account from Google authenticator app, you'll not be able to recover it by adb systems.

Simply go to Google my account, log in, and if it asks for authenticator pass code, choose a different methods of verification, and then either backup codes or through mobile verification (whichever you've got active). Then switch off authenticator system of verification. Again switch it on, and follow on-screen processes. Done. This is the simplest method to regain authenticator access.