This is specific to TX not to be documented per Paul Arens (1/5/2016)
To manage which users are assigned to a group, follow these steps:
From Setup > Groups, search to find group(s), or click the down arrow next to the Search button and select Show all results. Select the group(s) you want to edit.
Open the task list and select Assign Users to Groups. Click Start.
Enter text in Authorized Users to begin searching for users. Select the users to assign to the group. Click Assign to selected groups.