Tagged Vlans on Asus RT-AC66U IPTV

[Ralms]

Hi there,

Im from portugal and my ISP is Portugal Telecom which provides me with the service called Meo. 

The router they supply is a thomson that I dont consider being good enough since its 65mbs wireless and not that strong in terms of Lan but I want to use it as a dummie for the TV (IPTV box) and phone.

So after searching around the web I found some different approaches to my issue that is getting the service to work with the Asus router only.

The info I gathered was that since its fiber, it works with VLans. Vlan 10 for Internet and Vlan 12 for IPTV and phone. And some other stuff that is not important so far.

So what is my issue, I want to put the Thomson router to manage phone and IPTV but for that to work I need to send it tagged Vlans or otherwise it wont connect. 
At the moment internet works since at in menu Lan + IPTV I set up internet as VLAN 10 and everything works fine. But having port4 with vlan 12 doesnt seem to be enought.
Im using Merlins build 3.0.0.4.374.39 and I would like to know if someone can tell me the commands to get my Lan port 4 with Vlan 12 tagged. 

Thanks.