Before you go that far, just unplug the white battery and connect a battery (or BCR) to the battery connector and power the loco up (10V). Make sure the boards actually work before you go further.
A lot of those under board mounted batteries have some provision for the battery to be slid out the side, whether still in the holder or the holder stays and just the battery comes out. Look around the holder for a screw thats holding it down and see if its accessible. I dont know if I've ever been in a PS-1 F-3, but there are a lot of engines that were set up like that and you dont need to remove the boards to change the battery.
Otherwise, it would be the screws in the gold bracket holding the board set to the frame that would need to come out. If you have to undo those, dont move the board any more than you have to in order to get the battery out.
Regardless of how it comes out, put a BCR in it.