How do we bring back the rental car from alamo at the o'hare Chicago airport? Are there signs we can follow when we drive up to the airport?

Its tricky. Make the quick first left when you follow signs for car rental returns.

We used our GPS and it took us directly back to Alamo at O'Hare airport.

Yes, follow the signs for "rental car return"

Yes

I drove by GPS. Signs were only near Alamo

We did not pick it up at o'hare so there is no map

There are signs for car rental return.

Try to find map you've get with rental agreement. You can easy find where to drop off the car by following instructions from the map.