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Your first step would be to rename that group. For instance if you have Social Studies per 1 group, you might want to rename it SSper1. To rename a group, click on the group, then click on Group Settings and change the name. One of the reasons to rename your group is that you cannot create groups with the same name. Then after renaming the group, you should archive the group.
To archive the group, click on the group you are going to archive. On the right hand side, click on Group Settings. You will notice a button at the bottom of the box that says Archive Group. By archiving that group, no one else will be able to join the group but the teacher can access the group if it is necessary. Then the teacher can create a new group (with the original name) and all the files and links the teacher had in the original group will still be available in that group.