How to edit the Contact List

I have attempted to edit the email address of a Contact but the program will not accept the change. What am I doing wrong?

Highlight the Contact … double click it or click on EDIT at top of list, make change and then click on SAVE & CLOSE button in upper left corner of screen.

Thank you for the reply. I have done what you suggested but what I get is the corrected entry replaced with a “nobody@invalid.invalid” entry when I click on the SAVE & CLOSE button. Closing the CONTACT LIST and reopening it makes no difference. Closing the email program and reopening the CONTACT LIST makes no difference. Rebooting the PC and reopening the CONTACT LIST makes no difference. I’m at a loss as to what to do next.