Reducing Echo across channels

For a recent project, I have two audio channels, one recorded directly from a mixer and one mic recording the audience. The audience mic picked up a lot of the audio from the speaker that the mixer was connected to, making it hard to make the audience audible without bringing up a terrible echo. I've used the sound removal tool before and found it extremely helpful, but it requires audio that is less than 100 seconds, and the track is an hour long. Is there any way I can use the track from the mixer as a reference to reduce the echo in the room? Thanks!