I would go to Documents folder. There should be "Elder Scrolls Online" folder there. Rename it, to something different. When you start the launcher next time, it will re-create new folder and basically "reset" game to default settings.
@Tommy_The_Gun so for example. If I renamed "Elder Scrolls Online" to "Backup" and that did not fix anything. Then I could delete the new instance of "Elder Scrolls Online" and rename "Backup" to "Elder Scrolls Online" and that should be like nothing ever happened like restoring a file back up, correct?