There are works on the railway line in this period, from Domodossola there is a replacement bus to Milan. Check for the timetable trenitalia.com or sbb.ch

IF not the shortest time is needed there is a very nice -swiss views, mountains, lakes, tunnels, kind of detour_ the tiny local FART/SSIF train from an outer part of Domo-stazione to Locarno, change-Lugano-change-then either direct train to Milano (pay that 11€), or via Chiasso=change again on local treni.

Only as far as Domo you do NOT need to pat the 11€ extra fee, as as far as that is considered a swiss tariff-point.

What mcadv says is certainly true. It is a lovely ride and well worth the extended journey time to use the FART service. One of the sets they use is an observation train and there is a supplement of 2.5 euros paid to the conductor. Well worth it in my opinion!

We are traveling from Zermatt to Milano Centrale so I would take a regional train to Brig then take the FART train from Brig to Lugano? Then take the fast train from Lugano to Milano Centrale? Sorry for all the questions, I find the trains a bit confusing. 

We know trains in Europe can be a bit confusing. Firstly use the RailPlanner app to get an idea of timings. Then check them on the country website so use the SBB app to find trains all the way to Locarno. The use Trenitalia for services to Milano.  There are changes at Visp Domodossola Locarno. This is something you can easily check for yourself! Where we can help is giving you information you could not find out for example at Domodossola keep walking down the platform ignoring where everyone else goes until you reach a stairway down to the FART platforms (no lifts). Locarno FART station is below the main station so use the lift to go up to it. You should find Zermatt depart at 09:13 arrive in Milano at 16:17. There is a spare hour in the schedule to enjoy either Domodossola or Locarno. No reservations compulsory on any of these trains. The only train you can reserve on is IC6 from Visp and they can do this for you in Zermatt if you are worried.

Hi yes this route is also possible and it is more scenic. And so you don't have to use the replacement bus to Milan.

Like others say, FART railway from Domodossola is under the "normal" railway station.

From Locarno there is every hour a regional express RE80 train to Milano Centrale. No reservation needed or possible. If you have time I would suggest to visit Locarno as a small break.