Disconnect the black plug (electrical) from the selector valve in the trunk. It'* located between the right rear passenger seat back and right rear strut tower behind the carpet. Cylinder looking thing with 3 airlines going to it as well as electricity. After disconnecting it, deflate the rear struts through the schrader valve for the utility inflater.
The selector valve being disconnected isolates the struts from the rest of the system, and allows you to manually fill/deflate by the inflator valve.