How to delete saved passwords and usernames on an iPhone, iPad, or iPod touch – AppleToolBox
If the password manager gets it wrong and saves the wrong stuff. Go to settings/password & accounts/website & app passwords and then you can see them all, edit and swipe to delete
Learn how to delete saved passwords and usernames from Safari and other apps on your iPhone, iPad, or iPod touch. It's easy!
— Read on appletoolbox.com/ios-7-delete-saved-usernames-passwords-ipad-iphone/