D4 key problem

Another problem on daughters D4. They were given two keys when they bought the car but one was a total mess with buttons missing. They bought a new key surround/case and carefully removed the chip from the broken button version and put it in the new case with a new battery. It looks very smart as you’d expect but it doesn’t work. Do you have to program the key to the car? Can it be fixed? Any hints as to what to do to try and sort this out?