The only thing you can and should do is to dispose of the car seat in a way that would prevent its future use, or rather would make it impossible. The reason for that is that a car seat that has been in a crash cannot be considered a safety device. It is extremely hazardous to use it and most certainly pointless. The only exception is a minor car crash, where the car itself has suffered no real damage and airbags, provided they are installed, have not been deployed.
If you are curious about what else constitutes a minor car crash, we recommend checking out safercar.gov/parents/carseats/using-car-seat-after-crash.htm
Keep in mind that even one mismatch means that the car seat should be replaced. As for what you should do with the old one, we suggest that you check out this short article of ours.