You see this board that says A2?
Carefully remove the cables, unscrew the two big screws up and down and slide it out towards you.
Inside you will find the two NiCd packs. These need to be replaced in order for the robot to keep the mastering.
But for now, there is no software in the robot.
Do you have a laptop, serial cable with DB25 plug and a backup file with the extension .lmd?