What is the routing printed on your ticket? Normally there is a βVIAβ line on the ticket somewhere. And who did you buy the ticket from?
Generally if you want to change a ticket before you are travelling you need to contact the point of sales. If you miss a connection during travel you deal with the operator directly on the spot. In this part of Europe if you miss a connection you just take the next one. No need to change a ticket. Those busses and the train to Chur all run every half hour.
In this case I would not worry to much. The connection times are not short. The one in Feldkirch is even ridiculously long. You will have no problem finding the buses, everything is well signposted.
And you will actually set foot in Liechtenstein! Lots of tourists go out of their way to be able to do this!