Scnf tickets

Don't know. What tickets are you talking about?

I am booking tickets from Strasbourg to colmar on scnf app and it says
Ticket non exchangeable refundable until the day before departure

No idea. When we went to Strasbourg from Colmar my wife and I just got a group day ticket good for 5 one way trips. It was cheaper than individual tickets. We just bought it at the train station.

I can't imagine why you have to book that train ahead of time, just get tickets at the station when you go. The trains go every 1/2 hour and take about 1/2 hr between the two towns.

I believe those are TER trains that are not reservable. Which is why you can get a refund but not exchange them - there would be no need to exchange them, if you miss a train or change your desired departure time, just take another train.

If you have a TER ticket, you can ride any TER train between your departure point and your destination on your travel date. If you want to change the travel date then you would get a refund and buy a new ticket. I think that is what is meant by the ticket is refundable but not exchangeable. You don't need to exchange your ticket on your travel date. You just use it for the train that you want.

Thank you very helpful

If I take a later train than the one I booked can I just use the code for the purchased ticket on my phone or do I need a new ticket

The ticket is good for any train at anytime that day and not limited to the time you booked. You just show the QR code and the conductor scans it. You don't need a new ticket.