Hi there, are you an administrator for your Duo account? If so, utilize the following directions. If not, you will need to work with your Duo Administrator to reorganize devices if the self-service portal is not enabled.
Because our RD Gateway integration exclusively uses our auto-push functionality, it will always send a push or phone call authentication request to the push- or phone-call-capable 2FA device at the top of the user’s “Phones” device list on their user page in the Duo Admin Panel.
If you want to receive a push or phone call on a different device, drag that device to the top of the Phones list. Note that auto-push always prioritizes sending a push notification over a phone call.
It sounds like the other user needs to install and activate Duo Mobile on their smartphone, and then they will receive automatic pushes when logging in. If they have Duo Mobile installed on one of their 2FA devices, but it is listed below a phone without Duo Mobile, try dragging the device with Duo Mobile installed above the phone-only device in their Phones list.