You must be a site owner before you can perform this steps
- Click on the gear icon on the upper right corner of the screen.
- Select Site Permissions.
- On the right panel that appears, select "Advanced permission settings".
- On the next page, click on Create Group at the ribbon section of the page.
- Enter the Group Name, set the Owner to the current Owners group.
- (Optional) You may assign the permission to this site.