changing 1 device from 5g to 2.4g

INSTRUCTIONS (T Life app)

Some devices, such as printers, have trouble connecting to the gateway’s default configuration.

You can have several Wi-Fi networks on the gateway.  You want to leave the default network alone (2.4 & 5 GHz; WPA2/WPA3 and AES security) and add a second, dedicated 2.4 GHz network.  This second network is for devices that can’t connect to the default network.

Using the T Life app on your phone: Tap Connect (at the bottom).  Tap Things (at the top).  Tap your Gateway. Tap the magenta button Manage.  Tap Network (at the top).  Tap the magenta + Add Network.

You should now have an "Add new network" page.  Under General details, Enter a new Wi-Fi network name (SSID) and a password.  Under Advanced settings, change the Frequency Band to 2.4 GHz.  Under WPA Version, change WPA Version to WPA/WPA2.  The WPA Encryption Mode should automatically change to TKIP+AES.  Tap Save at the bottom. Use this new network for your LED lights.

Use the default network for your other devices, as much as possible.  Note that WPA/WPA2 (on the second network) is less secure, so I recommend setting this network to be Hidden. You can hide it after you get your devices connected to it. (The Hidden switch is in Advanced settings, below WPA Encryption Mode.)