In Ableton, let's say you have H3000 Factory on audio track 4 and you want audio track 3 to be the sidechain signal.
1. select View > In/Out so you can view the IO section of each track
2. In the "Audio To" section of track 3 (sidechain track) select "4-audio" in the top dropdown menu, and "sidechain-H3000" in the bottom dropdown menu.
That should work.