Allow your insert to cool to room temperature and the clean out your fireplace insert using a broom and dustpan or turn off the gas, if applicable.
Put a drop cloth over the hearth and into the insert itself.
Put on a dust mask, goggles and leather gloves. Plug a trouble light into a near-by electrical outlet and turn the light on.
Lay on the drop cloth over the hearth, placing your head inside the fireplace insert. Shine the trouble light up into the chimney and locate the retaining bolts holding the damper in place.
Fit a wrench with an appropriate sized socket and unfasten the retaining bolts with the wrench and socket holding the damper in place.
Turn the damper sideways once you remove the bolts and pull it out of the fireplace insert. You can now install a replacement damper.