Mirror laptop screen not external monitor, please help! :-/

Hi all,

Would appreciate your help. I'm trying to setup 3 x external monitors with my 2020 intel MacBook air on Catalina 10.15.7. I'm using an external USB-C hub with 2 x HDMI and 1 x VGA port.

I have all 3 monitors working and displaying BUT the VGA monitor is mirroring one of my external displays, which is obviously useless. I'd like to mirror the laptop monitor, as shown in this diagram from the hub's supplier:

Can anyone, please, help me work this out and understand how to mirror the laptop NOT the external display?

Thanks so much in advance. I've tried apple live chat and phone chat but neither were able to help.

Jamie