You must be logged in as an Administrator to manage unallocated devices!
Steps
Navigate to the Manage Devices page on the left menu.
If you have unallocated devices, there will be a special banner at the top of the page:
To add a device to a group, click on the Allocate your device(s) button within the box.
The next page will list any devices that aren't part of a group:
Tap the Add button next to every device you want to add to a particular group - every device you select will be added to the same group.
On the next page you will select the group your devices will be added to. You can either create a new group (and enter a name for the group) or select from one of the existing groups:
To select a device individually click on the radio button to the left of the ‘device name’, to select all devices click on the radio button to the left of ‘Select all’.
You can now choose which group you would like to add the device(s) to from the drop-down menu. Once you have chosen the group, click on Add to group.
If you would like to create a new group, then select Create new group from the drop-down menu.
You will now need to give this new group a Name.
Once you are happy with the name, click on Add to group and your unallocated device(s) will be added to this new group.