PLEASE HELP–URGENT

I was following some instructions on the below page and reset the WordPress Address URL and Site URL to include an “s” in http and saved it. Now I can’d access my website at all, just get a File Not Found Error. How can I fix this? I am not to tech savvy so explicit instructions would help.

Thank you.

https://make.wordpress.org/support/user-manual/web-publishing/https-for-wordpress/