many couplers have a rotating adjustment scheme so you can tightent he 3-4 jaws ont he fitting. see if yours does and loosen it.
inthe mean time, tap a ez out into the zerk and extract.
them make a combi tool that has a grease fitting wrench, thread chase and extractor flute.. but you don't need that tool to get them out usually.
if just the tip broke. use a wrench. if it sheared at the threads.. use the extractor.
sometimes an appropriate screwdriver ( flat blade) will drive in and bak them out.
so will a left handed drill bit too.