How to assign users to groups

No way to add new members to groups?

As @rehe mentioned, the tab ‘Groups’ in admin has disappeared. OK, I found it in the hamburger, but before it disappeared from the admin page, it was possible to add news users right here. See below.

Now, when I access “Groups” from the hamburger, I can’t find any link/button allowing me to add new users to a group. See below.

Can somebody, please help?