(edit the pf.conf and insert following codes)
You are all set!v6_wan_if="your-v6-wan-interface-name" v6_wan_ip="your-v6-wan-ip-address" no nat on $v6_wan_if inet6 from $v6_wan_ip to any nat on $v6_wan_if inet6 from any to any -> $v6_wan_ip
You are all set!v6_wan_if="your-v6-wan-interface-name" v6_wan_ip="your-v6-wan-ip-address" no nat on $v6_wan_if inet6 from $v6_wan_ip to any nat on $v6_wan_if inet6 from any to any -> $v6_wan_ip