Sentry Mode will save off triggered "events" (motion or sound activated) recordings during parking automatically to the SavedClips folder. However for anything that is encountered while you are driving that you want to Keep, you need to manually save it. Very important distinction if you haven't read the manual on this.
So while in driving mode and something happens (you get hit, you want to capture footage of bad driving, etc) you need to depress the camera icon (which should have the red light on it to indicate that it is actively recording). A press on the icon will show up as a download happening. The dashcam saved function will take the last 10 minutes of live footage while the car is on and transfer it from the 1-hour buffer, which records over itself btw, and saves it off in the TeslaCam folder to SavedClips folder. It's date and time stamped. BIG NOTE OF CAUTION when saving off a video, for safety's sake I'd say give the camera two minutes immediately after the incident has occurred to make sure the camera isn't midstream writing to the SavedClips folder or the video can be truncated and you could loose that incident. A number of us have had this happen to them including myself when there was a vehicle I wanted to go back and see. Didn't give it enough time to finish writing and sure enough the saved clip I thought I had, cut off prior to the moment I wanted. So best to not press to save immediately. The camera writes in 1-minute blocks and you can't be sure where in that one minute it is in recording time.
Since this could be an important video to have, I suggest everyone try ahead of time saving something and checking your SavedClips folder afterward to get acquainted with what to expect from the dashcam.
OP sorry but it sounds like you didn't save the 10-minutes off. There can be times where the material you want can still be available in the RecentClips folder (the 1-hour buffer) if it hasn't been written over yet, so always worth a look there too if it hasn't been that long. But if you've been driving longer than an hour after the moment has occurred TeslaCam will have overwritten the buffered video and you'll be out of luck. Always best to save the recording shortly after it happens, as SavedClips do not get written over until you manually delete them from your USB drive media.
If you forgot to manually save off to the SavedClips folder and realize this before the one hour of buffer time is up, you could Stop the dashcam from recording by pressing down on the TeslaCam icon until you see kind of a digital wave disperse across that small area of the screen by the icon. When I've turned off the camera I've been able to see the "wave" on the left side of the camera so I depress the icon with my finger slightly to the right side of it. When my finger has been directly over it sometimes it has covered up the "wave" action and I didn't see that it actually had stopped. In any event the camera icon should now show a camera but with no red dot indicating it has shut down. If you pulled your USB drive now, you'll want to look for that footage in the RecentClips folder and if need be transfer it to your computer. The one-minute files will be date and time stamped there as well.