Overcooked macarons are actually really easy to fix unless you go all the way and burn them, in which case, there's probably no salvaging that. But if they are a little brown around the edges and too crispy, still fill and assemble the macarons as usual and let them mature for 2 or 3 days. The older they get, the softer they will be thanks to the shell absorbing some of the moisture of the filling! Not only will the cookies soften up, but the flavors will develop better as well making them even more delicious!