Download Simplified Social Share Module for phpBB 3.1.x.
Copy the folder social9 included in the downloaded .ZIP file to the folder ext of your phpBB forum. After having copied the folder you must have an ext/social9/simplifiedsocialshare folder in your phpBB directory.
Login to your phpBB administration control panel (ACP) and open the Customise tab. Then look for the Simplified Social Share extension and click on the Enable link to activate it.
After that, Clear your phpBB cache. Please follow the given steps :
Login to your phpBB Administration control Panel(ACP).
Click on the General tab.
Press the button Run Now next to Purge the cache, Confirm your decision and your cache will be refreshed.
Login to your phpBB administration control panel (ACP), navigate to the Extensions tab and click on the Sharing Settings link in the Simplified Social Share group.