Knocking when pedling mid gears

Hi,

I recently just got the smart bike and have started using it with Zwift. Unfortunately, I have come across an issue that I am looking for advice on.

When riding I constantly feel like I need to be in the highest gear as any time I go even into mid gears the flywheel feels like it is running away from me and my pedals knock when I ''catch up'. Just too be honest I am new to this and perhaps there is something that needs to be set up that I missed so am looking for some advice.

Cheers