Q: hi

You need to remember your encryption password to turn it off : About encrypted backups in iTunes - Apple Support

You can't use an encrypted backup if you don't have the password. If you forgot your password, the only way to turn off backup encryption on your device is to erase your device and set up as new. Erasing removes all data from your device. If you don't want to erase your device, restore from an iCloud backup instead.

Delete all content from the phone i.e. reset it back to factory defaults (after copying off anything that you want to keep e.g. documents, photos) : How to erase your iOS device and then set it up as a new device or restore it from backups - Apple Support