Start with quick checks: is the site URL right, are the database name, user,...

https://victoriasmasterchat.yousher.com/my-wordpress-site-shows-a-database-error-but-my-other-sites-on-the-same-host-work

Start with quick checks: is the site URL right, are the database name, user, and password right, and is your host up? If so, try deeper fixes, like a database repair. Contact hosting support if the server is down or your login details fail again.