Here you see the flap that lets in the warmed air, and the thermostat sticking out at the lower right.


To remove the flap and thermostat assembly, squeeze the two holes together, releasing the tabs.


A snap ring plier is handy.


Here's the replacement challenge.


Squeeze the spring to remove the old thermostat.


Install a new one, or a nail cut to resemble a new one, for a permanent solution.