Ejecting an avatar from a group is done more or less the same way it is using the official SL viewer.
- Select the "Groups" tab
- Highlight the group you need by clicking on it from the list of groups
- Click on the blue "Info" button to bring up the "Group information" window (seen below)
- Click on the "Members & Roles" tab
- Highlight the avatar name you want to eject by clicking on it from the list of member avatars
- Click on the red "Eject from Group" button