There is such a tool as a 'broken tap' removal tool... I once had to buy one and use it... If the tap isn't too tightly embedded it will work...

https://www.brownells.com/gunsmith-t...nt=952-400-014

You might be able to 'make something that will work if you get four small nail (which fit into the grooves of the tap, but not too tightly), then use pliers and grab all four nails and TURN the tap out (if you're lucky)...