Find your nearest wildlife rehabilitator. They cannot legally give out veterinary help, but if you surrender your duck and somehow readopt the same one later on they will often help. If you cannot get your baby to help then it is possible to relocate a hip. It’s been a while so start by applying a cool cloth to reduce swelling for about five minutes. From there gently stretch out the leg to normal position, GENTLY using your thumb to press the hip back in the direction of the socket. Chamomile tea is a surprisingly effective pain reliever if you have nothing else. Best of luck with your baby.