The hats and masks in the set are smart props. If you have Genesis selected then load the props they will position themselves close to where they should be on Genesis. Just use the Trans/Scale dials to get a close fit. The items don’t need to conform like clothing items since they are static items like real masks and hats. Fortunately the items act like conforming clothing in that they move with Genesis when you pose Genesis.
There are 6 sets of five items that are sized to fit Freak, Hiro, Kids, M4, The Girl and V4 so just pick a set that is close to your Genesis’ head shape and tweak it from there.
These two examples are with an M5+Hyde character wearing hats and masks from the M4 set. The flower is parented to the hat and can be removed or hidden if desired.