Go to the hamburger menu and click Admin > Users > Export (You can export any of the active, new, staff, etc.)
Once the export is done you should get a system notification with the .csv file in a zip folder
On Excel or Google Spreadsheets import the file
Once the file opens up go to the user column and depending on the OS either (Windows) left click + shift or (iOS) left click + command to select the usernames you’d like and copy them
Go to the Admin > Users > Group > + New Group
Under ‘Members’ paste the copied usernames. They should separate automatically!
Here is a video too of how it looks after I’ve copied them from the .csv file: