Question about Non Stop Backup and choosing the storage partition manually

When I started Non-Stop backup for the first time, itl asked which partition to back up, but would not allow me to choose the destination. I have 4 drives attached, and it chose a drive with the most free space, which is NOT the drive I want to use. The amount of data on Drive C is 50 GB out of 223 GB, and the drive I want to use as the nonstop backup destination has 257 GB free space.
How can I choose to use that drive instead of the one that was chosen by the porgram without asking me???

Thanks

George Klabin