Memory card or expansion pak?
If it’s official, either way you’re you’re going to need a special screwdriver to open it. It’s not something most people have unless you purposefully buy it. You can find them on ebay for very cheap, a few bucks.
If you can’t get one, you can try to make one out of melting the tip of an empty pen. Then immediately stick it on the head of the screw. The plastic should conform to the screw head. Wait for it to cool and you may be able to open it that way. Just make sure you don’t breathe the fumes.
BTW, if you’re talking about the memory card not saving your games, your battery is probably dead. These batteries are 20+ years old and all have to be replaced eventually.