How do I fix the loose samsung chromebook plus bottom panel

You will need a PHILIPS Size 0 screwdriver to remove the back panel. You will have to remove the 8 screws on the back (there are none under the plastic feet), then you will need a plastic card so you can stick it between the body and the cover, then slide the card around the sides to pop them out, after that you can just separate the hinge-side of the panel from the body with your hands. However, putting the cover back on is much harder. iFixit Guide: How to disable the touchscreen on a Samsung Chromebook Plus

Skip steps 4, 5, and 6.