Airsoft !!!!!!!!!!!!!!!!!!!!!!!!!!!?

hey guys i was trying to put a new handel on my airsof dboyz m4 so i took out the moter did all of the stuff put it back in but it would only fire full auto so i tryed to fix it but when i closed the gun i heard a crunch when i opened it back up my black wire was severd from the other pice what should i do will a airsoft store fix it for me and how much will it cost thanks