<<"I didn’t think to look at the timetable but I shall. Thank you for the heads up! ">>
<<"I can take a train from St. Gallen to Chur and then the Bernina Express from there to Tirano correct?
How would I get from Tirano to Zermatt? From what I can tell I need to take the Bernina Express bus I believe to get to Lugano and then take a train from Lugano to Zermatt">>
You have a good part of the answer at your finger tips. Please learn to use the timetable.
As the instruction page that I linked you to above states:
<<"Enter your departure location, the arrival location, the travel date (day. month. year) and travel time (24 hour format, so 5 PM is 17:00). You can optionally enter a "via location" if you prefer a specific route and not necessarily the quickest route. Click the button to find all travel options. The location name can be a train station, bus stop, boat dock, cable car station or street address.">>
That is a subtle way of saying that the timetable defaults to the fastest route unless you plug in a "via" or several "Vias."
So, try St Gall to Chur to Tirano, and see what you get.
I did and I get two choices every hour.
The Bernina Express does that route, as do regular trains:
I did did not check the all the timetable links to see which one is the Bernina Express, and I don't know if that special train over that route runs at a certain time that I missed.
From the page I linked-
<<"The winter timetable of the Bernina Express is limited. There is only one train per day from Chur to Tirano and back, and an occasional one from St. Moritz to Tirano and back. Also, the Bernina Express bus from Tirano to Lugano does not operate. See the timetable for details. But there's something extra too: the regular trains from St. Moritz to Tirano have a panoramic car attached. This concept is called Bernina Panorama Winter. You can sit there after paying a supplement, and enjoy the superb winter scenery in a very comfortable manner.">>
April could likely still be winter.
Regular trains run all year but have train changes.
In order to put in the "vias" you need some understanding of the basic geography and where the trains run.
There different ways to figure that out, but the one that I personally prefer is to use Mapsearch.CH.
Start with the overview, then zoom in:
It lets you see the overall geography, especially if you use the aerial view. Then, if you zoom in to zoom level 32, the train lines appear prominently. It helps you with setting up reasonable routes that may not backtrack.
The simplest and most direct route from Luganio toZermatt is indeed the bus. However, I don't know if it runs in April on whichever dates you choose. The paragraph that I quoted says in does not run in Winter, and says that Spring starts in May for that line. So, it probably does not run.
So, I pick my date and try the timetable. Then, I pick a date in the Summer and try the timetable to see what happens. If you find the routte in Summer but not in April, that's a clue.
Italy first makes sense, but it sill won't get you on much of the alpine mountain transport, as Alpenrose has noted.