It very much depends on the train!

If it’s one where reservation isn’t necessary, you just jump on the next train. It’s always worth checking what the next train is - have a plan B

If it’sa train where you need reservations, it gets more difficult. You can make a reservation for the new train, and refund your unused one. Or you can ask station staff for help.

 Post the journeys you’re worried about, and we can give you specific adviice.

22 February, Muenchen Hbf 15.28 to Wien Hbf 19.32

and then change to Wien Hbf 19.42 to Bucharest Nord 15.26 

That will usually work because the train from Munich is usually on time, looking at the past weeks. But it was also cancelled a few times and delayed 40 minutes once, for which the night train didn't wait.

I'd take an earlier train from Munich.

I agree.

If you miss the 1942, you have to wait until the next day for the next train to Bucharest. Definitely take an earlier train to a Vienna.

It is possible to cancel an Interrail seat reservation for witch i used the DiscoverEU pass, and used the pass for seat reservation to other train?

I doubt it. Maybe it's in the DiscoverEU FAQ somewhere?

In any case, I doubt a reservation is really necessary from Munich to Vienna on the 22nd. But if you want one and you don't have any free ones anymore, it's only €3 on tickets.oebb.at.

Yeah...the problem is i have to change the whole route...which is Paris est 9.06- 12.16 Mannheim hbf 12.30- 15.14 Muenchen hbf 15.28- 19.32 Wein hbf 19.42 - 15.26 Bucharest nord. 

Two of them doesn't require seat reservation, which is fine, but the first one, Paris est- Mannheim requires, and I used my Eurail credits for it... If I want to leave earlier, with the train Paris est 7.18- 10.59 Frankfurt (main) hbf, i have to pay for the seat reservation in order to catch the night train from Wein hbf to Bucharest.

It is worth to keep the first reservation or it is better to change the route?

There’s no way I would attempt that itinerary via Mannheim and Munich, especially before a sleeper.

I would go earlier from Paris on the ICE9571 departing 0654. Connect in Stuttgart or Karlsruhe, and leave time for delays.

On 22/2, there's no train Mannheim 12:30 - München 15:14. Maybe there was a timetable change, I can't say.

If you leave Paris at 9:06, you'll miss your night train for sure.

Please check timetables on on bahn.com, never in the DiscoverEU Travel app.

I think the best you can do is contact customer service and ask them to rebook the reservation from Paris because your timetable doesn't work anymore:

https://helpcentre.start-discover.eu/hc/en-gb/requests/new