Putting 12V on a 9V LED is not good. Probably good for 1/2 second.
Because we don't know how much power the LED uses, or any vital information we need to experiment.
Put a meter across the 9V LED and add a 100 ohm resistor to the 12V source. The meter probably will read 6V and the light will be very low. Try 51 ohms, 22 ohms, 10 ohms. Play this the resistor until the meter reads about 9V. (8.5 to 9.5) You might try a 100 ohm power "pot" and dial in the value. If the meter reads high and the light is bright cut the power now! and try a higher value.