Congratulations @thearena it’s a sweet, sweet unit. I cherish mine.
The problem to overcome is that when you connect an audio interface to a phone the person on the other end of the line hears their voice coming back to them as an echo and that can also get captured in the recording too.
As @craigconstantine says, engaging the mix-minus button fixes that. Except the H6 does not have a mix-minus function. So we use a hack that produces the same result as mix-minus. In short, we make a stereo recording where your voice is panned onto one channel (maybe the Left) and your guest is panned on the other (the Right or vice versa).
This is the video that taught me how to do it. Pay extra care to ensure you use mono cables/adapters where he says so. Mono jacks or cables have one black ring. They can be a pain to source so if you have a local instrument store nearby it might be worth a visit.
The biggest danger is that all those cables make electrical interference a real danger. If you hear a hum then move the wires and H6 well away from your computer. And keep the wires as apart from each other as possible. This happened for me from time to time so set everything up well in advance of your interview to make sure you have time to fix this if it happens. Make sure everyone with access to your desk knows they will die if they mess with your set-up.
But it is effective and records good sound because the big, big, big upside is that you can adjust the levels in real-time, for each track, live while recording. So in practice, because I still use Zoom.us, the Zoom.us recording is my backup and my mix-minus Zoom H6 recording from the SD card is my primary recording.
The whole mix-minus setup should have no effect on the recording from whatever vid-conference service you are using.
Just one other thing - despite what the thumbnail on the vid says you can only record one remote guest this way. Any other tracks will be in the same room as you via the XLR connections.
Have fun!!!