The functionality to delete on Facebook Messenger doesn't exist, however the only way to clear the search history is to sign out of Messenger completely. Because Messenger has no "sign out" button, you have to use the Facebook full app to kill your session. if you don't have the Facebook app you will have to download it from the Apple Store all from the Android store.
Once you have the app, follow these instructions to sign out:
- On the bottom right click the menu item. If you using an Android click the menu icon on the top right corner.
- Look for a section called "Settings & Privacy" near the bottom of the list and then choose "Settings"
- Under the security section click on "Security and Login".
- Under "where you are logged in" you see a list of all the Facebook sessions including the one on Messenger.
- Choose the messenger option then Press Logout. This will log you out of Facebook Messenger.
- Now go back to the Facebook Messenger app. When you open the app you see a message that says session expired.
- Press ok and then login again.
- Your search history has now been deleted successfully.
In future we advise you to search using the Facebook Main App because the search history in the main app to delete.