Re-pair Apple Remote to LG Smart TV

The Apple TV Remote (Siri Remote) pairs with the Apple TV box, not with TVs.

The Siri Remote can do volume control for select TVs, if supported and configured to do so, through IR. It doesn’t require bluetooth pairing with that TV.

If the volume buttons on the Siri Remote do not change the volume (anymore), then you may need to restart just the remote: If the volume buttons on your Apple TV remote aren't working - Apple Support

Else also verify the volume control options in the Apple TV Settings.

So I have to use TV remote control to power the set on.

Turning on the Apple TV box may also wake the TV from standby, if HDMI-CEC is activated on both devices.

For the Apple TV box: Settings﹥Remotes and Devices﹥Control TVs and Receivers﹥On

or: Settings﹥Remotes and Devices﹥Turn On Your TV with Your Remote﹥On

For the TV: See its manual on CEC. Manufacturers may use their own trade name for CEC, e.g. LG often uses the name ‘SimpLink’.

Alright, enjoy your Apple TV and its remote.

Through CEC, the input selection could be automatic for the then powered-on device in the HDMI chain. If you turn on your setup by waking the Apple TV box through its remote, then the TV could have the Apple TV box as default input, thus showing the Apple TV Home Screen immediately.

You have this box connected to your TV through HDMI, correct?

If your LG TV remote has this Input or Source button, then press that button and select the corresponding HDMI port (e.g. HDMI 1, HDMI 2, …) from the on-screen menu.

After selecting the input for the Apple TV box, you should get to see the Apple TV Home Screen, which has its own app tiles.