Remove the grip frame by removing the two screws that hold on the tube. Be careful of the safety spring as you remove the frame. Don't lose the spring or detent ball. Remove the side plate. Slide the safety out.
Buy or make a brass safety and stick it in the hole the original came out of. Replace the side plate. Using a little grease stick the detent ball and spring back in the frame. The grease will hold it in place. Put the grip frame back up to the tube and reinstall the screws.