With high ambient temperatures your freezer is certainly working harder and longer to maintain temperature inside the unit. That will shorten its lifespan.

As for what to do about it? Have a basement or room in the house? If it is not already, you could insulate the garage but insulation only slows the transfer of heat. Ventilation will help but only when the outside temperature is below that of the garage. You'll also need a fairly large fan to make a significant difference.

In a chest type freezer the evaporator coils (cooling coils) are right under the interior lining of the food cavity then there is a thick insulation layer and the condenser coils are wrapped around the outside of the insulation immediately under the exterior sheet metal skin of the freezer. The condenser coils are tight against the exterior skin and the skin acts as a heat sink to help dissipate the excess heat energy to the outside air surrounding the freezer. The heat your feeling is normal operation.

Keep the coils clean.

Get a box fan and have it blow right on the sides of the freezer. It's all a matter of how fast you can transfer the heat. As long as the garage is cooler than the sides of the freezer it will help. 100 deg. is cooler than 120 deg.

I would move it to an inside wall - as far away from the door and any windows as possible. I don't think a fan would do much but blow hot air. Maybe one of those attic type fans in your garage ceiling could help pull the hot air out of the garage. Plant trees/shrubs around the exterior to help keep it cooler