The YouTube app on your Android device retains your search history, much like the desktop version of the website. Clearing this history is fairly simple, and this tutorial will walk you through the necessary steps.
How to delete your YouTube history?
Open your YouTube for Android app, and click on your profile picture. From there, tap Settings, and next choose History & Privacy.
Tap Clear search history and then OK.
If you want to delete your watched videos, choose Clear watch history.
Note: Keep in mind that if you don't want your app to ever keep track of your search history, you can disable this feature by checking the box next to Never remember history.