Remove the following screws securing the antenna plate to the mini:

Two 6.6 mm T8 Torx screws

Two 5.0 mm T8 Torx or 2.0 mm Hex screws (either screwdriver will work)

When putting back together:

It can be difficult to get the hard drive seated correctly such that the antenna plate fits in place correctly. If the screw holes don't line up with those on the hard drive, make sure that the two pins that are in the back of the hard drive are properly seated in the holes at the back of the case, above the housing for the second hard drive.

The antenna attaches directly to the hard drive (red markers), therefore attaching the antenna can move the hard drive around and loosen the connection of the hard drive cable to the logic board.