2 suggestion I did before...
1. stop the return pump, siphon the water from overflow until lower level so that easier to catch the fish. this method a bit tedious but fast and straight forward....
2. if your tank height allowed. slow down the overflow let the water level increase higher than overflow.. your fish will swim out for food eventually. this method need patient and may take a few day for fish to coming out.
Your tank got aggressive fishes?
Cheers and Happy Reefing..