For band steering to work properly:
The SSID and Wireless Security settings for 2.4 GHz and 5 GHz should be the same.
Make sure to enable Band Steering. The new firmware gives more Band Steering options compared to the old system. The old system only has Enabled and Disabled. The new options are the following: Force 5 GHz, Prefer 5 GHz and Band Balance. To know how each option works, please click on this link.
Make sure that the transmit power on the 2.4 GHz is higher than the 5 GHz. For example, if the transmit power on 2.4 GHz is 14 dBm, put the 5 GHz on 20 dBm. This will make the coverage cell similar for both bands. This is very critical for Band Steering to work properly. For other best practice wireless configuration, please click this link.
To know the benefits of band steering, please click on this link.