The best way to do this would be to export the original group list from the admin panel and then import them as a CSV back into the admin panel you.
Here's how you do this:
- Click on the group you would like to export from the "Groups" tab
- Click on the "Members" tab at the top of that group
- Click "Export as CSV"
- Once exported, click on the "Members" section in the left hand menu
- Click "Import as CSV"
- Select the Group you wish to add the previous group to from the drop down list
- Upload CSV
Once you finish that process, it will add all of the members from your original group to the new group you selected from the drop down list.
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