Need Help with Redirection after changing the domain of my Discourse Forum

Assuming you’re going to remove the current forum, it’s just a normal Apache or nginx redirect.

For nginx

server {
    server_name original.example.com;
    location / {
        rewrite ^/(.*)$ https://new.example.com/$1 permanent;
    }
}

or Apache

RewriteEngine On
RewriteRule ^(.*)$ https://new.example.com/$1 [R=301,L]

I had missed the part where you’re only moving Discourse and not migrating. Since you’re only moving domains, you don’t need the permalink redirects.