Be careful about formating the HDD.
If you had it connected when you installed Windows onto the SSD some files may have been installed to the HDD and Windows will be broken if you format.
The HDD should have been disconnected when you installed to the SSD.
If the drive wasn't initialised there's no chance any files from the Windows install process would be on it. Agree any installs should be done with only the boot disk plugged in, just good practice