You need to increase the spring pre-load. That would be the 2 adjusting rings (closest to the spring). Sounds like you have your pre-load set to basically zero. Tighten the top ring (raise it up, forcing the spring to compress and thereby increasing the stiffness and reducing the suspension travel) and once you have the pre-load set where you like it, bring the middle ring up against the top ring and tighten the rings together so they are locked together (turn the rings in opposite directions, ideally holding the top ring in place while raising the middle ring). This will set your pre-load. Doing so should also increase the ride height of your Supra. After this is done, you can adjust the bottom ring upwards so it becomes basically free floating and then rotate the shock shaft by turning the upper and middle rings together. This will pull up your shock's bottom half, causing your ride to be lower. Once you have your ride height set where you want it, adjust the bottom ring down to where it meets the lower half of the shock and tighten it against the tube.
You may have to do this several times to get it where you want, I know I have.
