Easy steps are:
Connect the hard drive, using external usb is fine also.
Using Windows CMD (dos command prompt)
Type in command: diskpart
Then command: list disk
Then select the disk you want to wipe and sell: select disk 1
Then command: clean
Make sure you clean the correct drive. After clean is done, go to “Computer Management” then “Initialize” the hard drive and then “Quick format” is good enough. Your hard drive now wiped clean, next to impossible to recover any data unless you’re like the FBI with millions dollars equipment and tools like the manufacturer even them will be a challenge, no need long deep MRB low level formatting.