...the car? The guy at the dealership said that this type of garage door opener has a revolving code, and that he didn't know how to do it. The manual instructions doesn't work.

I don't know if its model year specific but the following isntructions worked fine for my garage door opener (rolling code type)

Press the two outside two buttons on your rearview mirror for 20 seconds, or untill the light beside the buttons starts to flash.

Find the "learn" button on your garage door opener. It will be on the unit itself, not the handheld transmitter.

Press the "learn" button on garage door opener, right after pressing that learn button press the button on your rearview mirror that you wish to open your garage door...Hold button in for 2 seconds.

After a few seconds repeat pressing and holding the rearview mirror button for 2 seconds again.

and Viola' you should be good to go. Be sure to have your ignition key turned to the on position and you may want to unhook the garage door from the carrier to avoid and suprises.