http://ciisqbg45nggykdl6rjdrq3wc64csga4vkphu66qsi65mypeitqedoad.onion/pfsense
Select "Manual Outband NAT rule generation", then click the Save button, then Accept Changes. Afterwards, click the the first Add button at the bottom. Set Interface to OpenVPN, Address Family to IPv4 (or if using the IPv6 VPN IP, to IPv4+IPv6). Set Source to LAN Subnets, leave every other option at their defaults, then click the Save button at the bottom, then the Apply Changes button.