enable rewrite and modify root folder

Question

Hello connoisseurs of Nginx I would like to enable the rewrite and modify root folder

what permission command and how to do this successfully because when accessing download the file instead of displaying and I am frustrated c/ so little content found.

my code:

   server {
    listen 80;
    server_name example.com www.example.com;
    return 301 https://www.$host$request_uri;
}
server {
    listen 443 ssl http2;
    ssl_certificate /etc/letsencrypt/live/example.com/fullchain.pem;
    ssl_certificate_key /etc/letsencrypt/live/example.com/privkey.pem;
    ssl_trusted_certificate /etc/letsencrypt/live/example.com/chain.pem;
    include snippets/ssl.conf;
    include snippets/letsencrypt.conf;
    root /var/www/html;
    index index.html index.php index.htm index.nginx-debian.html;
    server_name example.com www.example.com;
    location / {
            try_files $uri $uri/ =404;
    }
}

php 7.4 installed