"General Settings" change has changed appearance theme

I got a blog on my own domain (https://paseosmadrid.com/), and on General Settings, I had both, the WordPress Address, and the Website Address, pointing to the domain name.
By mistake I have changed the WordPress Address, and point it to the URL that I had the blog before on WordPress,as https://fotosmadrid.wordpress.com.
When I want to change this back as I had it, it won’t allow me. The worst part of it is that the appearance of the blog on its domain, has lost the theme somehow, and it looks as if it doesn’t have a theme at all.

I find no way to fix this, or to go back to the original General Settings page, to change this.

I would appreciate your help on this,

Thanks