Getting a 404 error message from Nginx

I would check the virtual host file for your domain and verify that the "root" path is pointing to the directory where your website files exist. For example, here's an entry from my website's virtual host file:

root /var/www/public_html/test_server;

You can also test your Nginx configuration using the following command:

nginx -t

We also have a few guides that you can reference regarding Nginx and how it's configured. I've provided some links for your reference:
https://www.linode.com/docs/web-servers/nginx/how-to-configure-nginx/#location-blocks
https://www.linode.com/docs/web-servers/nginx/nginx-installation-and-basic-setup/#set-your-site-s-root-directory