Add or Manage Devices After Duo Enrollment
You can add a new authentication device or manage your existing devices through the Duo Prompt.
you can add additional verification methods, manage your existing devices, or reactivate Duo Mobile for Duo Push from the Duo Universal Prompt.
When logging in to an application with the Universal Prompt, click the Other options link on the authentication page to view your list of available methods. If your organization enabled self-service device management then you'll see a Manage devices choice at the end of the list. Click that to enter the device management portal.

After approving a Duo authentication request, you can see all your registered devices in the device management portal.
View the full instructions here: https://guide.duo.com/universal-enrollment#add-or-manage-devices