Take a look  at the Swiss railway map and you see why it is difficult to get to Chur from Lugano—- hut is far ro the east.
https://cdn-doc.myswissalps.com/docs/default-source/rail-network-maps/swisstravelpass.pdf?sfvrsn=7788603a_56
You could connect to the Glacier Express by taking a train north from Lugano to  Göschenen on the Gotthard Pass route.  There is only one direct train a day, the Gotthard Panorama E press, departing Luganomat 9:18 (reservations required).   There are other trains with a single change at Bellinzona ( the TrenomGottardo) or Altdorf (after the deep tunnel).
Change at Göschenen to a train going the short distance to Andermatt, one of the few stops on the Glacier Express. Check  the SBB schedules carefully for the timing as there are only 2;or 3 Glacier Express trains a day.  There are other, regional trains on that route that you could take, but there will  be additional changes along the way.