Not familiar with your base but if it's a one pice base, you should not have anchoring the base with the ramianing screws and leave the bad one as is. Now, you can go ahead and fix the bad hole and there is more than one way to make this fix. usually when you mount a reciever base it's pretty much going to stay put, for the optics. Your problem is quite common as there is not a much metal on the upper wall of the reciever. Take care not to use to long of a screw as it might cause the bolt, to drag or malfunction. ....
One fix is to retap for and oversized screw. Then there are additional options on what to do next, like locktite blue or double sticky tape and such.
Be Safe !!!