How can we change the default version in the plugin?
I couldn't find that in the documentation.
You need switch to the customer interface, then in the "domains" section, you'll see a new menu on left, labeled "PHP Switcher". Through this interface, you can switch between various PHP versions, on a per site basis. You need just to select the site on which you want operate on, then select the PHP version you want use. On selection, the frontEnd will automatically schedule a PHP version change.