Using a resistor to help regulator heat dissipation
The regulator needs rougly 7.5V-8V on the input, so you can drop 4-4.5V with a resistor. Rough calculation to drop 4.5V at 0.9A means about 5 ohm resistor, and it needs to handle dissipation of 4 watts. That can be split into multiple resistors too. But regulator would still dissipate about 3W which is a lot. Consider a 7805 compatible switch mode regulator module.