I suppose your hostel/hotel has a printer and they can print it.
Beside should be also fine to show the reservation on your phone (is there a QR code on it?! then makes no difference)

These OeBB tickets are in the format of the normal CIV INtern tickets-and in AT/OeBB ditto for inland-over Verbund/Landesgrenze. IF it is only for a seat-then do not bother, just jot down the car/seat nr-there is also NO bar/QR-code. Seats are also not marked-so you will need persistence if there is already some ignorant sitting.

For a real sleeper it might however well be advisable to print it out-that can be done at any OeBB machine-of course only In AT. If not-just use google: print shop in a town you spend some time in whilst going toward Zúri