Select the HDToolbox icon and choose "Icon Information" from the menu. Add a tooltype reading
SCSI_DEVICE_NAME=xyz.device
where xyz.device is the name of the driver for your HDD controller. HDToolbox by default uses scsi.device which is the default for most Commodore HDD controllers. Third party controllers might use other names like oktagon.device or similar. The manual of your controller should tell you the correct name.
Depending on the age of your controller it might also be that HDtoolbox does not work with it at all but you have to use the software which came with the controller.
Bye,
Thomas