There is no need to do that and it won’t help. As said above, discourse-setup will do a test to see that it can talk to itself using the host name. If you edited /etc/hosts before you ran discourse setup then dns didn’t work and you didn’t get a certificate from let’s encrypt and that’s why the web server won’t start up. If you try enough times you’ll get rate limited and need to wait a week or use a different subdomain.
You call look at /var/discourse/shared/logs/var-log/nginx/access.log (or something very much like that) to see the problem.
Easiest thing at this point is to use a new subdomain, set up dns, wait for it to propagate (there are tools that will show you) and then run discourse-setup.