When put my car in reserve my lights work on one side. Both brake lights work and turn signals work.

Check your bulbs on the bad side. If bulbs appear good, follow the ground wire. Could be a bad ground. If you have a volt meter or test light, see if the socket is getting 12 volts. If not, could be a bad ground or broken wire.

I took it to a car place and they said all the lights are working sometimes the left side reserve light and brake light dont work. If its wiring is that expensive to fix

Sounds like you have a bad ground. It's not like they will have to rewire the entire system. It will just run you money for the amount of time it takes the shop to trace back the wires to the faulty ground. They will probably just sand down the grounding point and put on a new connection.

Okay thank you so much for your help ill call my mechanic and let him no whats going on. Thanks again @