This type of switch doesn't have specific ground lugs like your pancaked 'import' style PBG switch. Typically, the metal switch frame will be grounded by the cavity shielding.
As such, you will need to connect the bridge and neck pup grounds to either the back of a pot or just run a short wire from a pot ground point and link it to the pup grounds at the switch (then insulate the join so it can't short) etc. The latter means that you don't have to strip the pup wires back a ton so the grounds will reach, if you get what I mean.