As long as the chick isn't with a bunch of others who are super-pecky, you may be surprised at how well a gash will heal on its own. Bandaging a chick does not seem to work well - there's never really a good way to attach a bandage, and the chick will go nuts trying to get rid of it. Plus they're so small and delicate that stitches aren't really appropriate.
The wound should dry up / crust over fairly quickly. You may want to apply some betadyne / iodine with a cotton swab or tiny paintbrush, and adding tetracycline (oxytetracycline) to the drinking water is a good idea to stop it getting infected while the gash heals.
To make a little chick dose up on tetracycline I've found it helpful to take a pop bottle cap full of water, mix in enough oxytetracycline powder to make a fairly noticable yellow color (about a pinch of powder) ... pick up the chick and the bottle cap, gently dunk its beak in the medicine and then let it raise its head and swallow it down... repeat a couple times. Do this a couple times a day for 3 - 5 days. (Make a fresh bottle cap of medicine each day.) The alternative is to medicate all the chicks' drinking water,
Best - exop
