This GitHub Gist details the manual configuration needed on a UniFi controller to enable IPv6 tunneling with Hurricane Electric's Tunnelbroker service.
This is what works for me personally. Stuff you'll need to do to adapt this to your ends:
- Replace "local-ip" with your USG's public IPv4 address.
- Replace "remote-ip" with the address of your Tunnelbroker tunnel server.
- Replace "address" with the IPv6 address that your are allocated.