Beginner - How to allow FTP from internet to DMZ

Hi everyone, 

very sorry, but I'm really new to the Sophos Firewalls.

I've just got the XG 125 with total protect and setup a basic config consisting of a DMZ, Internal Lan and internet connection.

I'm trying to find out how to allow FTP traffic from the internet to a server in my DMZ.

I've already managed to expose web traffic to the internet using the Business rule, WAF application template.

Also permitted my internal Lan to have any : any to the DMZ. (for RDP, ftp testing etc.)

I've also started looking at the routing, and created a policy routing from WAN > DMZ for FTP service. but still no joy.

Any pointers would be really appreciated.

Best regard

Dave