The instructions apply to the TikTok app for Android and iOS.
How to See Your Watch History on TikTok
TapProfilein the lower-right corner.
TapMenu(the three lines) in the upper-right corner.

You’ll see all of the videos you’ve watched in the previous 180 days in chronological order.
Tap a video to watch it again.
Videos automatically leave your watch list after 180 days.

Go to your watch history and tapSelect.
Tap the videos you want to remove (or chooseSelect all watch history), then tapDelete.
From theHometab, tap theSearchicon (the magnifying glass).

Enter a keyword related to the video (the title, creator, topic, etc.)
Tap themenubutton to the right of the search bar, then selectFilters.
TapApplyto restrict the results to only the videos you’ve previously watched.