Depends on how you got them, from whom and what it says on them.

IF you got a kind of long code AND from MAV, then it MAY be possible to have it printed out at a MAV machine (there are plenty in all main stations). If it is a normal mail, with attached ticket (with bar or QR-code) then you have to find some internetshop or ask in your HTL if they can arrange it-or if not, where you can have it done. THis certainly has to be done that way if you got it from Oebb-in that case can only print it out In Austria from one of their machines.

Where did you buy the reservations?

I bought them through eurail page. They were sent to my hotel but for any reason they were returned to the sender. I need the printed reservations because I will take a night train. I really don´t know what to do :(

You need to make a complaint with Eurail so that you get the money back. Use the form below.

https://eurail.zendesk.com/hc/en-001/requests/new

Then you need to buy new a reservation.

@rvdborgt @Angelo What is the best way to buy a new reservation?

It depends from the nighttrain. If the nighttrain starts in Vienna you can book it online via ÖBB using ONE WAY TICKET OPTION and as discount Interrail/Eurail Global Pass. If the train starts in Budapest then only at the station possible. Maybe you can also buy it in other countries like Germany, Austria or Czech Republic.

We're so sorry that your reservations did not reach you in time. Please reach out to our customer service team via email on customerservice@interrail.eu or customerservice@eurail.com and be sure to include your reservation number. You can also cancel the tickets in your account overview so that the seats can be made available again. Our team will refund this for you. Tickets for this journey are generally only issued in paper format, so we recommend reserving this locally at the station. 

Note for future travellers: never cancel any reservations yourself when they don't reach you in time, since that is a cancelation by you, which will cost money if at all possible. Just request a full refund from customer service.