You need to make sure you have DNS setup for www and have it pointing to the same server. It can be an A record pointing to the same IP. Then you’ll want to edit the Nginx file and add a location block for it: https://www.hostinger.com/tutorials/nginx-redirect/
server { server_name www.soapbox.tld; return 301 $scheme://soapbox.tld$request_uri; }