When changing your device(with the same number) although your DUO app will transfer it must be reconnected by following the steps below. 

Open an application that requires a Duo authentication(ex: MyClasses, Gullnet).

After entering your user name and password you will be prompted for Duo verification.

 

At the Duo Authentication screen select My Settings & Devices.  

Choose Enter a Passcode and you will see a prompt below in blue to select Text Me New Codes.

You will receive a text from DUO with a long list of numbers.  

Enter the first code in the sequence received by text into the field provided then click Log In.  It should begin with a 1 and be 7 digits in length. 

Select Device Options  in blue next to your phone number.

Select Reactivate Duo Mobile to have your new device activated using the same mobile number.

You may be prompted to Verify Ownership of your phone number.  Click Text Me, enter the 6-digit code received in box 2, then click Continue.  

Choose the device type as either iPhone, Android, etc.

A QR code will be presented on screen.

*If you initiated reactivation by logging into an app (GullNet/MyClasses) on your phone,  you will need to select Take me to DUO instead at the bottom in blue.  You will be taken to the DUO app on your phone and your account will activate automatically. 

*If you initiated reactivation by logging into an app (GullNet/MyClasses) on a PC, you will need to scan the QR code with your phone. 

Install and open the Duo Mobile App on your device then press Add+ to add the account to your DUO app.

Upon installation of DUO you will be asked for permission to use the camera.  You must allow DUO to use your camera in order to scan the activation code.

Select Use QR code then hold your camera to the QR code for it to scan.

Select Save after naming the account. 

Once you receive the green check mark your device is now reactivated for Duo Mobile press the continue button to continue with logging in.

You will now be able to send yourself a Push request when logging in and approve via the DUO app on your phone. Below is an example of the prompt you will receive on your phone.