If they're just backing out a bit, take them out, put a little 5200 in the hole and tighten them back up.
If they are stripped, you will need to remove the screws and fill in the hole with epoxy. A jello shooter syringe works great for this. Just save the shooters until
after the work is done.
Every screw in my deck stripped out a while back and I had to use this method of repair. So far they are all staying put, but I had one hell of a hangover the next day.