Separating usb audio from mics sound on Tascam M12

Hi,

I have an Issue recording through usb on my Tascam M12: i'm recording a podcast using regular mics in a studio, and i have guests on a Zoom Call or Google meet. i want to be able to record the incoming sound from the call - separated from the online call.

for example - two host are talking in the studio, one guest is on Google Meet. each mic in the studio is being recorded separately, but everything that is going on is recorded in the PC channel set to record the Google Meet. 

That makes editing the guest nearly impossible.

I'm using Tascam M12 with firmware update V.141

My usb input is routed through input 9/10 

please help.

Thx