Ferrule Tite or hot glue. There may be enough glue in the pocket to reset the coin, excess will keep it from seating all the way.
When I reset a coin I will put a few shavings of either of the above mentioned glues in the hole, align the coin, then press down on the coin with a heated bolt head. Not red hot as that will bubble the finish next to the coin. I learned the hard way that just any bolt head will not do. You need to take a little time and file or grind the grade markings off of the bolt head prior to use. Otherwise, you can dent and ruin your medallion. I now keep just such a bolt in my supply drawer for just that purpose. This method only works for the metal coins. Do not use it on the plastic convex shaped medallions or you will melt them.