Rocket kicker? Into the hitch hiker?
The two screws on top of the playfield holding the plastic piece down right at the rocket launcher also give you a LARGE amount of adjustment for the metal plate at the rocket launcher.
Two times I've enlarged the slot in the metal plate with a needle file to get just a bit more adjustment, but alignment with the hitch hiker shot is mostly the metal plate.
Level first. This is one of those adjustments that can 'dial in' a machine and make for an extraordinary play... or an average playing game. So level the machine properly, then adjust the plate.
If your machine is quite a bit out of level, and the plate at the rocket launcher is quite a bit out of alignment I would expect a lot of 'bounce outs' and missed hitch hiker shots.