Accidentally changed SiteURL

Hello everyone. This is an emergency. I was in the Settings on Dashboard. I was experimenting, and changed the SITE URL to my website that I’m building on my local host. It was http://localhost/agape and I changed it to one of the links that were withing my site http://localhost/agape/the-chatter-box . I can’t find how to change it back. Because anytime I attempt to goto settings or anywhere, it gives me the message “Ooops… Error 404
Were sorry, but the page you are looking for doesnt exist.”

Please let me know how I can repair this without losing any data.