If you are an organization admin, you can assign a device (or devices) to a network as you create a new network or you can add them at a later time to an existing network.
Assign a device upon network creation
When creating a new network, the second panel in the form has a dropdown menu where you can select as many devices as you would like to add to the new network (see figure below). In order for a device to appear in the dropdown menu, it must be owned by the current organization and it must not belong to any other networks. If the device is owned by another network, you will need to transfer the device, rather than assign it at network creation.
Assign a device to an existing network
To assign a device to an existing network, navigate to your organization Devices page. Select one or more devices to assign and click the Assign to Network button in the modal that appears near the bottom of the screen (see figure below).
After clicking Assign to Network, you will see a dropdown menu that includes all existing networks within the organization. Select the network you would like to transfer the devices to and click Assign to Network.
For a video walk-through of this process, please see the video below: