Here is a video and step by step instructions with screenshots are below.
During the authentication process, select Add a new device to enroll additional devices or My Settings & Devices to adjust device settings.

It is strongly recommended that you enroll more than one device in case your primary device becomes unavailable. (A good option for a secondary device is your office phone.)
To enroll additional devices:
- Click on Add a new device
- Confirm your identity by authenticating with one of your devices
- Follow instructions to enroll a new device (see Enroll a device with Duo)
- You now have multiple devices enrolled
- If necessary, set a new device as the default (or primary) device
- During authentication, you are presented with a list of devices. Select one to authenticate.

To manage your devices:
- Click on My Settings & Devices
- Confirm your identity by authenticating with one of your previously enrolled devices
- From the Settings window, you can identify a default device, as well as rename and delete devices
