How to set up DNS on hover + fortrabbit ??

In the hover control panel, go to your domain and click on edit. Then click on the DNS tab, and add an A record with hostname @ and value will be the IP address of your fortrabbit server.

If you want www.domain.com as well, add a CNAME record with hostname www and value of domain.com.

Then it's a matter of making sure your fortrabbit server is setup to listen for the domain name (not sure on how to do this part, I've not used fortrabbit myself).