Tonya will appear on the map once again ("T" with a small question mark on the map) and asks Franklin to do one last job. Get in a vehicle with her and head to the impound lot to pick up the Towtruck. You'll get a report of an accident, so head to the scene to find a car that hit a pole.
It's a little tricky to hook up the car to the Towtruck from the front, as there's a pole in the way, so go to the back of the car and hook it there. Once you have it connected, bring it to the auto repair shop and unhook it. After you're finished, bring Tonya back to the impound lot to finish the mission.