Your mixer has an alt 3/4 bus which is a second pair of outputs that a channel gets sent to when you press its mute button… A good way to go is:
-Plug your OT into the mixer, plug your mixers alt 3/4 outputs into an OT input pair, and press mute/alt3-4 on what ever synth or multiple synths you want to send to OT. You’ll need the OT setup to monitor the synths as they will be sent to OT and you’ll want them to come out of OT which will then flow to your mixer out the mains and into the interface. There’s multiple ways to do this on OT depending on use case but the easiest is to turn up the Mixer Dir parameter all the way. Just never mute/alt34 the OT channel as that’s a feedback loop…
There’s other awesome configs you can do with an OT/vlz/interface setup but they’re more complex so I’d probably start there for now…