Have you gotten a new smartphone, but kept your original number? Did you have to reset your phone? Or did you accidentally delete the Duo Mobile App? If any of these apply to you, don’t worry! You can easily reactivate your Duo Mobile app, even if it was the only device you had registered.
Login to a Duo protected service (like any of the G Suite apps). Once you get to the Duo Authentication screen, choose the “My Settings & Devices” option on the left.
You will have to authenticate to verify your identity. Simply choose one of your other registered methods to authenticate. If your smartphone was your only registered device and you still have the same number, you can still have Duo call you to authenticate.
Once you have verified your identity you will be shown a list of your devices. Click on the “Device Options” button next to your smartphone and then click to “Reactivate Duo Mobile.”
You will be walked through the same questions about your device as when you originally registered that number with Duo Mobile. Just make sure that if your phone type/operating system has changed that you choose the options for your current phone.
You will be prompted to download the free Duo Mobile App. Once that is downloaded and open, click to continue. In the app on your phone make sure to click the “+” to add a new service and use the app on your phone to take a picture of the QR code at appears on your computer screen. You may have to allow Duo to use your phone's camera to do so.
You are all set! At the bottom of your device options page you can click the “Back to Login” button and continue to login to your account as usual.