You can't do alot but yes you can reduce it.
1) use silver parachute curtains along garage walls and opening it will reduce radiation
2) Install 2 exhaust fans in your garage and keep them running
3) use sunshades in car for side, back and front
4) use a microfiber top cover as it traps air which disable conduction taking place
5) don't close windows completely leave a small gap
6) from local source get roof heat treatment done
Follow these points they will surely help you
On a lighter note:
Ac lagwalen garage mei