How Do You Remove Outdated Backup Locations

I do a manual backup to a portable Hard Drive in addition to the automatic backup to my C:/ drive. However, I have replaced the original portable drive with a different one, and the file location and drive letter for the manual backup have changed. When I select "Change" after selecting Cntrl-B, the outdated backup location appears in the drop-down list. of backup locations in addition to the new location which I have added How do I permanently delete the outdated location from the drop-down list?