In my experience, temporarily disabling or renaming 5Ghz on your WiFi router is the best solution.
Assuming your 2.4Ghz and 5Ghz signals share an SSID and subnet, you can follow these instructions:
- Disable 5Ghz on your router or rename the 5Ghz signal to a different SSID, while keeping the 2.4Ghz SSID the same as before, like from SSID_name (for both 2.4 and 5) to SSID_name and SSID_5.
- Set up your 2.4Ghz device.
- When setup is completed and your device is connected, re-enable your 5Ghz signal or rename your 5Ghz SSID to match the 2.4Ghz SSID.
The point of temporarially renaming or disabling only the 5Ghz is that you will keep the same SSID for all currently connected devices, 2.4Ghz and 5Ghz. Changing both SSIDs means that all devices will have to connect to a new network.
Your 2.4Ghz-only devices will stay connected to 2.4Ghz and your 5Ghz-capable devices will choose the best of both frequencies. Generally speaking, the only time you'll see weirdness like this is while setting up a smart device, which is what you are doing.