Be careful not to damage the concave seat.
This type of repair must be perfect for obvious reasons.
if you are very lucky, you may get the old nipple out.
Failing that, drill, remove and tap.
Or drill out and fit a helicoil.
Last option and probably the best, but most expensive is to fit a good pre owned caliper.
Plenty preowned calipers in stock and good to go same/next day if required.
Just drop me a PM if I can help further.
Alex.