If you look at the edge of the antenna plate near the Mac mini body, you'll see a groove where the metal from the unibody fits. I found that if you turn the mini around so the antenna plate is closest to you and us the pointy end of a spudger to lift and place the antenna plate, you can get this groove to fit properly and the screws pop into place.

I use the foam service wedge from iFixit at my work office but doing repairs while working from home during the pandemic I’ve found that a roll of paper towels works well too.

I’ve found that loosening the T10 screws on the enclosure to the left helps give some room to remove and reinstall the drive. Otherwise reattaching the SATA cable can be a hassle.