Problem connecting Calex device to Telekom Magenta router (Unable to separate 2.4 GHz and 5 GHz bands)

I am having a serious problem connecting a Calex device, such as a bulb or lamp that requires the 2.4 GHz band, to the home Wi-Fi network provided by a Telekom Magenta router.

The main issue is that the router's software does not allow for manually separating the frequencies into distinct 2.4 GHz and 5 GHz networks, because the router broadcasts both frequencies simultaneously under the same name and manages them automatically.

In this situation, I have no way to physically force my phone or the router to switch exclusively to the 2.4 GHz band during the pairing process, and furthermore, I cannot take the device and walk to another room to cut off the stronger 5 GHz signal, as the entire setup and pairing process keeps dropping or ending in an error.

I would greatly appreciate information on how to successfully install a Calex device under these conditions, given that it absolutely requires a 2.4 GHz network to function properly, while the router makes separating these bands impossible.