If you are coming from San Francisco, take the San Bruno exit (marked rental car return). If you need to gas up, turn right instead of left at the light. After refueling, you turn left and go back over the freeway, and make a right at first road (a T) and follow to the rental return.

Hertz is on the bottom floor, follow signs, return and get on the train.

Painless, only issue is time. Leave yourself time for traffic and the various waits and you will be fine