1) Login to WHM with root user.
2) Once logged at your left hand side menu search under software section click on MultiPHP Manager.
3) On your right hand side pane , you will see the list of websites hosted on the server. Select the website for which you want to change the PHP version
4) From the “PHP Version” drop down window select PHP version that you want to configure the website.
5) Now click on Apply in order to change the PHP version for the domain
6) You can now see that the PHP version for the selected domain is changed to PHP 7