First I would suggest updating your firmware to 3.4.5 by uploading this zip file to the system tab in DWC. https://github.com/Duet3D/RepRapFirmware/releases/download/3.4.5/Duet2and3Firmware-3.4.5.zip
Then have a read through this corexy setup guide.
https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuration_coreXY
There are motor tests described that may help you figure it out.