7912 Voltage Regulator
The thing about both the 7812 and 7912 is that the pin out is different as you are aware but there is a strong possibility that the 7912 you connected incorrectly is not actually damaged.

Pin 1 for the 7812 is the most positive pin i.e. Vin &amp; Pin 1 for the 7912 is also the most positive pin i.e. 0V

Pin 2 is the most negative for the 7812 i.e. 0V and pin 2 for the 7912 is also the most negative pin i.e. -Vin: -



Pin 3 is the output for both and sits naturally at a voltage somewhere between pin 1 and pin 2.

So, given the above, there is a strong case for assuming the regulator is undamaged and therefore reusable.