Not quite sure if there is a "defined process" for restoring grips. I have done some modest refinishing of wooden grips and have used suggestions on this forum ---- specifically, strip them in acetone, let them dry, fill any chips/cracks with a quality wood filler, stain selectively to blend imperfections, sand lightly with bronze wool (including very gentle cleaning of the medallions), and finish with tung oil or polyurethane. Others recut the checkering - I'm not at that skill level, but what I have done is turned some worn grips into rather decent "shooter grade" specimens.