Band steering won’t solve this problem. In fact, it may even confuse the 2.4GHz IoT devices more.
If you can’t set up the devices with the same SSID on both bands, it might be that your smartphone is connected to the 5GHz band but your IoT devices can only connect to the 2.4GHz band. You may use different SSIDs for 5GHz and 2.4GHz to solve this problem. Or, you may start with two different SSIDs to do the setup, then change the 5GHz SSID to be the same as the 2.4GHz one after you set up the IoT devices.