Admins use the Add Users to Groups tab in Manage Group Membership panel to add members to a design group and assign them Roles.
to display a horizontal menu. 
to open Manage Group Membership. Switch to the Add Users to Group tab. 
. The default role is Publisher. Use the pull-down menu to change the Role. You can not assign the Admin role to a member from this tab. Use Set up Account Admins.
Users must accept the invitation to join the group.