I would use some round wire of the same material and simply melt
it into the remaining prong. Then trim off the excess metal. If
you think this would be too dangerous, try the next-best thing.
Snip off a little wire, place it on your soldering pad & after
fluxing, melt it into a little ball. Then, taking a little
welding solder, flux, melt it and put the two together, pick that
up & solder it on top of your remaining prong. Trim and finish.
Best of luck;