If you're using the firewall extension you can go to Tools & Settings > Firewall, click on the plus to add a new rule and put in the information otherise since ubuntu uses ufw you can just use ufw commands to add the rules (ufw allow 9003 for example), although it's recommended that you just use the firewall extension that's within plesk for managing the rules since it's easier then having to ssh into the server to make the changes.