Go to the appropriate Duo Enrollment Page and log in with the appropriate credentials:
Click on My Settings & Devices.
Verify your identity. Since we’re reactivating Duo Mobile, Duo Push will not work. Instead, choose either Call Me or Passcode (which will send you a code via text message).
Click Device Options on the phone you are reactivating.
Click Reactivate Duo Mobile.
Choose a verification method and enter the code provided, click Verify, then click Continue.
Select your phone’s operating system, then click Continue.
Install the Duo Mobile app on your device if you have not already done so, then click Continue.
On your phone, open the Duo Mobile app. Click the “+” icon on the top of the screen. Hold your phone up to the computer and scan the on-screen barcode using the Duo Mobile application’s built-in scanner. After you have scanned the barcode, click Continue.