ok im being stupid but i cannot find the entrance to the resistance headquarters in the basemant in tunnel city.
i cant complete my last objective . can someone help me please?

if you mean subway town instead of tunnel city, than the entrance to the headquarters in under the empty car lift in the garage which is located right before the exit door. Just stand in front of the empty lift and it will open and an elevator will rise up. Once on the elevator you will have to hit the switch to lower yourself to the headquarters.

hope that helps you

In the garage, under the car lift