Locate and Mark ID. of APF.

With a utility knife, start cutting out traced hole. 

With tin snips cut out complete hole or drill with a 2 9/16" saw. 

Clean out insulation as required. 

Fill backside of flange with silicone. 

Install 2 self-starting screws across from each other, one for a safety line. 

ALSO SEE:

https://www.youtube.com/channel/UCXS2zRSvjnpsHJI5-EPm-sA