How to reset War Stories progress?

Because of unstable connection from Russia (I presume), my war stories are bugged.

Even though I have finished all of them, including collecting all the letters and challenges, on the main menu it shows me that I didn't do half of those.

So my question is there a way to reset the progress and try to complete them again?

Also on my first act of Tirailleur - Liberte none of the letters spawn, it shows the location but there are no letters there.