I have an 04 jeep wrangler i had an accadent got the body fixed but now the heater only works when i give the jeep gas but the fan works fine

There are two possibilities here. If the system is air bound or the coolant level is low it can act like that. Check to make sure coolant is full...If it is, remove the cap and start the engine and let it run till it reaches operating temp, keeping the heater on high heat setting.
After it is fully warmed up, add more coolant if necessary.
The other item is the vacuum system. If there is a minor vacuum leak, there may not be enough vacuum to open the control doors for the heater. Since it was hit, I'd check all vacuum connections, lines and also the vacuum reservoir behind the front bumper inside the right fender (most common location) to make sure everything is intact. The leak would have to be small though or the system would not work at all so look carefully.