http://ciisqbg45nggykdl6rjdrq3wc64csga4vkphu66qsi65mypeitqedoad.onion/pfsense
Scroll down some more until you see Gateway. Change this from Default to OPT1GW. Now click the Save then Apply Changes buttons. And if you're doing IPv6 too, go to Firewall -> Rules, select the LAN tab, then click the first Add button.