If you would like to clear browser history and website data in Safari, please consider to 

1. Uninstall a profile "Auto Filter Adult Content", and
   
   
2. Keep the Settings > School Policy > Blacklisted URL EMPTY

To Uninstall a profile, please go to 

1. Device > Device Management
2. Action/Bulk Actions > Settings > Uninstall Profiles
3. Select a profile
4. Confirm

To check Blacklisted URL, please go to 

1. Settings > School Policy > Blacklisted URL