To manage the Firewall rules:
3) Click on "Firewall" under the "Security" section
4) To modify rules, click on the "Modify Plesk Firewall Rules" button.
5) The list of existing rules will be displayed. Click on a rule name to modify it or "Add Custom Rule" to create a new rule
6) Once you're done updating your rules, click the "Apply Changes" button
If the Firewall isn't installed, visit the "How do I install new components in Plesk" FAQ for instructions on installing it.