Can't access the wordpress/wp-admin

Hi,

i’m not very expert using wordpress, but I faced the same issue on two websites I worked on:
https://www.redvalley.it – https://redvalley.it/wordpress
https://www.atlantideproject.com/ – https://www.atlantideproject.com/wordpress

After editing the “Website URL” and the “WordPress Website URL” from the general settings of the dashboard (from “https://www.redvalley.it/wordpress” to “https://www.redvalley.it/” in both of them), the website is no more available and it shows on https://www.redvalley.it
“www.redvalley.it
sito in costruzione

hosting su piattaforma Apache”

and ” ??

404 Page not found !

You’ve tried to reach a page that doesn’t exist or has moved.

← back home” with the menu in a white page, typing the URL https://www.redvalley.it/wordpress

Now I can’t access the admin page as everytime I try (through https://www.redvalley.it/wordpress/wp-admin ) it shows the same page of https://www.redvalley.it, so I’m not able to edit the permalinks and the General Options.
How can I fix the problem without losing the pages I already built?

Thanks in advance for your support