This one's tricky. Ostensibly, you can clear your history if you go to the "improve my recommendations" page, then click on "videos you've watched," and "Remove this from watched videos" the offending entries. You can also delete titles from the "Your Video Library" or "Your Watchlist" pages. Also remove them from "Your Browsing History," just to be safe.
If all you need is to cover your tracks on a video that your roommate will never click on, you're totally safe! But one problem persists: if she clicks on that same video someday, "continue watching" will show up instead of the standard "Episode 1 Watch Now." Even if you delete everything, you'll need to go into each episode and rewind it to the beginning, or risk people knowing that you watched Bosch. A gray bar will still appear under the video, but at least the green bar will be gone. So if someone is watching on a Fire Stick, they probably won't notice.
Now, we understand how mortifying it'd be if you really were caught watching Bosch, so we dug deeper -- and we found one of the most futile Amazon help threads in existence. Turns out no one knows how to do a full reset, although if you have a Samsung smart TV, you can sometimes get this to work just by deleting items from the list. If anyone figures out a more reliable technique, please go to this desperate, desperate thread and help these guys out (and us, really).
Another thing to be aware of: Amazon is the biggest snitch imaginable and sends emails to the account holder asking how you liked something after you watch it. Unfortunately, you can't disable these either, but if you delete your watch history right away, that should do the trick.