Wattbike Atom erg to gears

I’ve been using a Wattbike Atom for a while now and it works perfectly with the training plans in erg mode. However today I tried to do an FTP test and wanted to take manual control of the main effort. I dropped out of erg mode on Zwift but nothing I did would get the gears working raise the resistance manually.
The gears work fine in free ride.
Anyone know what I’m doing wrong and how I can take manual control mid training ride?

I would guess that you cannot switch from sim to erg mode during a ride - but I can be wrong.