The backup password is different from iPhone passcode or Apple ID, the only way is to brute-force it, it is too bad.iPhone backups can be encrypted with a password.
It appears that if the backup is encrypted and you lose the password, you're out of luck. Unless maybe you know someone at the CIA or the FSB.
[added] But before you give up, make sure it's not your Apple ID password that it's asking for. Try resetting that if you don't remember it, or think you might have mis-remembered it.
I've never tried to restore my iPhone backup, so I have no direct experience with this.
Thanks for the addupIs this your iPhone,you don't even remember if you have a password for iTunes.The only way is to recover password for iTunes.
Look what i found: https://www.androidphonesoft.com/resources/itunes-ask-for-backup-password-never-set.htmlI don't remember i have set any password for that. Does this sound normal?