How to replace the under seat amplifier (non-nav, jbl) in a 2010 Prius

Hi all

My car audio quit working completely - no car sounds except when it starts. No radio, Bluetooth (the head unit is an aftermarket android DIN). I have bought a replacement amplifier from eBay (86280-0W620), but I had to shelve the switch-out due to several other issues that got in the way. This was 3 months ago.

Now - I have no idea where I put the screws/bolts that I removed to take the old amplifier out. I also don’t understand the orientation of how the amplifier goes back under the front passenger seat. I also don’t understand how grounding works on this amp - I see no wire sticking out that can be clamped to a bolt or something.

I would really appreciate it if someone could help me out with some pictures/description of what the bolts that retain the brackets look like, and also the orientation of the amp under the car seat. Thanks.