ulm to varenna including the bernina express

I'd drop it in Lindau, as there will be a surcharge to drop in Switzerland. You can get a train from Lindau with a few changes.
If you want to do it in one day, the current schedule says take the 10:53 train from Lindau to Feldkirch, then Sargans. then Chur, then St Moritz, then Tirano (this is the actual Bernina Express with panorama cars and required reservations), then Varenna-Esino arriving at 7:36 pm.

wow long trip considering it only takes 4-5 hrs to drive, thank you

The fact that the train calls itself the Bernina Express is the hint that it is a very slow train. With a degree of upside-down logic all Swiss tourist trains which go very slowly due to the great scenery, the twists and turns of mountain railways, and the single track railway are named something Express.

If they went fast, you'd miss what you went for.

If a morning train is possibly more to your liking, you can do what we plan to do next year: arrive in Chur late the day before and take the morning Bernina Express from Chur to Tirano. According to https://www.rhb.ch/en/panoramic-trains/bernina-express , you can depart Chur at 08:32 AM with a scheduled arrival at Tirano at 12:45 PM. We then plan to travel immediately on to Varenna. The train we're looking at to do that (R 2569) departs Tirano at 13:08 PM and arrives at Varenna-Esino at 14:36 PM.

If you like rabs plan, maybe you could choose a hotel near the train station and get rid of the car that evening after you have unloaded at the hotel. We stayed at a 2 bed, 2 bath apt in varenna very near the little swimming beach... let me know if you want the link

thank you to everyone who has replied - you have been most helpful. Simone