If the alert or warning is recent you should see a small triangle with an exclamation mark (i think) at the top right close to the lte/bluetooth symbols. Press it and you should get the list of messages
Yep that’s how to see them and the Alert triangle is at the top of your screen. In fact had an alert a few days back (interestingly my husband on his car got the same one — saying our TeslaCam USBs were nearly full—kind of weird we both got the same alert at about the same time

), but here’s what the screen looked like when I touched the alert icon:
BTW neither of us was able to reformat in the car in this state. And when I inserted my USB drive in my laptop to use Apple’s Disk Utility to Erase to reformat, it wouldn’t allow that. Solved that issue by deleting 4 video files from one of the folders so guessing just not enough space to otherwise perform the function. Did not try selecting files to delete while USB was in the car. Drive did Reformatted after that though in my laptop.
I had thought I had read that the car’s TeslaCam software would delete oldest files automatically if you were getting low on space but that wasn’t apparently the case.