Here is the complete process for how to delete Facebook history on iPhone by following the steps. For this, launch the Facebook app on iPhone. Here, proceed to the search bar at the top of the screen and tap on it. You will see recent searches and list all searches you have done. In front of recent searches, you will find the option named edit and choose it. Click on clear search and tap on it. Lastly, it will ask you whether, you are sure; tap to confirm option to delete the search history.
To see this working, head to your live site.