Screw the mount on to the intake plate using the the two holes that are closest to the top.
Retract the plunger and slide the guide onto the "foot".
Cut about 1.5" from the end of the PTFE tube, and then put the end of the PTFE loop into the bottom of the guide. It's easier to slide the PTFE tube into the bottom of the guide before you put the gauge on the mount.
Put the short bit of tube you cut off into the top of the guide. It's necessary to have both tubes in so the filament is constrained everywhere but under the plunger.
Put the gauge onto the mount and twist the guide to face the plate so the filament enters it as straight as possible. Make sure the plunger still moves freely. You might need to trim the inside a little if the plunger is rubbing against the sides.