Once you’ve frozen a track that requires a sidechained effect, you’re faced with a decision. Do you need to keep the track frozen, or can it be flattened?
If you’re prepared to flatten the track, it’s very simple. Flatten the track, then drag the sidechain device from the track you temporarily parked it in back to the flattened track. This is the method I tend to use. When flattening, I also often use the workflow described in The Commitment Escape Hatch.
If you want to keep the track frozen, you’re faced with another problem: you can’t add a device to a frozen track. The simplest solution here is to Group the frozen track…
…then return the sidechained device to the Group track.