Organic Groups Mass Subscribe
Users can now be added in bulk to organic groups using Views Bulk Operations out of box. The simplest way to do this is to take the following steps:


Download Admin Views 
Edit the people listing page view at
/admin/structure/views/view/admin_views_user/edit 
In the view under
fields, select "Bulk operations: User" Under "Modify entity values",
be sure that either "All" or at least "Group Membership" is selected
Save the view if needed 
Go to /admin/people and filter the users as
desired Select "Change value" and click Execute
Under "Fields", select "Group membership", and select the group(s) you wish to assign the users to. 
Be sure the "Add new value(s) to Group membership, instead of overwriting the existing values" checkbox is checked or your users will lose their existing membership settings.
Click Next to complete the operation.