Try to check-in with Eurowings online later/ when you are in IST or enroute to DUS.

If you are checked in but no BP is issued it is no problem and you can proceed to the gate or get a BP at transfer desks at DUS, but if you are not checked in for the Eurowings there might be an issue upon arrival DUS because if you miss the check-in deadline. Try to check-in online as soon as you can connect your phone when landing at DUS or if wifi is available on the TK flight to DUS, try to check-in during the flight to DUS.