Steps To Clear Everything You Search OnFacebook in Facebook App:

1. First of all open the Facebook android app and then
open up your Facebook account from there. Then after
that tap on the Search bar in the Facebook android
app. You will now see all the recent searches in the
screen. There will be a Edit option available on the
right hand side of the screen. Select that option from
there.
2. After the first step you will now see the History of
all your searches on your screen. For clearing all
Facebook searches just select the Clear Searches
button in Activity Log and then confirm it.
3. That’s it! all your Facebook search history will be
removed/deleted.