what if you never received the prompt to set a new encryption password?
how do you turn off the local backup encryption?
That information is in the Related Article at the top of this page that you were reading when you posted.
If the device has already been erased the only option is to start guessing; you get unlimited guesses.
And you never receive a prompt to set a new encryption password unless you click Change Backup Password, and you need the old password to do that.