WD back-up won't recognize My Passport Drive

WD External Drives External Drives for PC
1

I got a new computer with Windows 10. I downloaded WD Discover and WD Back-up. When I launch Back-Up I select “back up files” but the program does not recognize the external dirve. I can see the external drive in my file directory so the computer knows it is there. How do I get the back-up program to recognize it?