lost password for backup file

Hi, its my first time on here and I hope someone can help. I have recently unlocked my 3GS from Orange because the network signal is very poor in my area, I am trying to restore from a backup now but a password that I must have set decades ago is not being recognised in iTunes. It has been a password that I simply cannot remember. Is there any way to reset this and allow the backup / restore to complete.

Thanks