Just remove the PF glass and then follow the switch chart on page 24 of the manual.
The diagram on page 25 shows the location of the switches, if you have trouble finding them.
You should be able to press on a target, for example, with your fingers and activate the associated switch.
Basically you're simulating the ball hitting the switch during a game.
Some switches may not be easy to get at, but the main ones we're interested in at this stage are the drop targets and the xwing targets which you should have no problem getting to.
Probably should also mention not to go poking around beneath the playfield with the power turned on unless you are sure of what you are doing. 
