IR control on new remote

I bought a new remote. The old black trackpad remote was still functional. I installed the new one, set the IR to control the volume on the sound system. It won’t control the sound (I see the white light on Apple TV flashing when I try), but the old remote still can change the volume on my sound system.

I’m stuck with 2 remotes to control it all. I can’t figure out to « uninstall » the old one or to get it forgotten on the Apple TV.