I have fixed a few bird's nests in my time. I take my stilleto and see if I can gently untangle enough extra thread to be able to knot and bury the ends in the sandwich. If you do it this way it is virtually impossible to find the boo boo. It only works if you can get about an inch 1-1/2 to work with. I also used a self-threading needle (the kind where you pull the threads into the end of the needle)because the ends are too short for a regular needle.
If the thread nest is too tight or not enough thread, I remove about 12 inches of the stitching, knot and bury the threads on both ends and re-stitch the line of sewing, knot and bury these ends too.