What is your departure time in Turin?
Looks like the TGV Turin - Chambéry has no pass holder seats left. You can book the one at 17:38 (28€ + 2€ booking fee) or book a normal ticket for the Frecciarossa at 15:41 (Interrail not valid, current available fare 59€ on www.trenitalia.com).
In the distant past-when people relied on printed timetables to take along-it would have been much easier to plan longer roundabout trips. This seems to have completely gone the way of the dodo-even though the printed EUR rail-timetable still exist and appears ev 3 monhtes fresh.
IF get stuck-and if you fancy a longer route with much more views and some distraction-and save any expesne: use regionale treni via Domodossola-Brig-Geneve-Lyon.
Have not yet used this app myself, but understand there is even a feature for plannign trips withOUT REServazione.