Answered: Forgot my iTunes backup password, how can I unlock my backup?

Unlike iCloud password, which you can reset by contacting Apple Support, there is no other way to solve the problem unless correct password was found. However, you can try as many as you can to guess out the password. If you already did that, then you need a program to scan the password in that backup file.

Here is a step by step guide on how to do that, please check: http://www.iseepassword.com/forgot-itunes-backup-password.html