steamfan1211 It is too early, the Gotthard tunnel will reopen in September and the new timetables are not known.
For the Bernina Express you can already buy a ticket between Zurich and Tirano and reserve your seat on www.berninaexpress.ch.
Between Tirano and Milan, it is also too early. You can buy the tickets later. You have only regional trains on this line, no discounts are available in advance and no seat reservations are possible.