If your magazine doesn't have the pull hole, and there are probably more variations of FAL magazine baseplates than any other magazine on the market,,, anyway,
Try inserting a thin flatblade screw driver into the clearance slot at the back.
It probably won't accept a whole lot of the blade but if you get enough in to start pulling down on the plate, as it starts to free up then use a 3/8" brass punch and hammer to start tapping the baseplate foreward off the magazine body.
No FAL magazine I have ever dealt with would allow the baseplate to slide off with hand pressure alone, they have to be tapped off.
If you didn't notice, this operation works a whole lot better if two people are involved. HTH