In Windows 7, click Start, type regedit in the Start Search box, and then press Enter.
In Windows 10, Windows 8.1, or Windows 8, press the Windows logo key+R to open the Run dialog box, type regedit.exe, and then click OK.
Repeat step 3 for any additional sets of credentials that have the word Outlook or Microsoft Office in the name. Then click Remove from Vault or Remove (depending upon which version of Windows you are running). And you can prove it to yourself by logging in to your Gmail account via the web, using the same password that you know is your correct password – the very same password that Gmail keeps rejecting in your efforts to POP your mail.