Buy a live trap, coon sized.
Place the trap in the garage.
Place some marshmellows in front of the trap and some more in the front of the trap and some in the rear of the trap. (Coons love marshmellows!!!!!!)
The coon enters the garage, sees the marshmellows, sniffs and then eats one, rapidly followed by eating more, enters the trap eating his way to the back, and in the process steps on the trigger and you have a live coon in the trap.
I use this method on my deck all the time and it works ALL THE TIME!
Trapping them is the easy part. Now you have to dispose of a live coon.
There will be many different answers for doing this- where you live, what your personal feeling are about killing a trapped animal, what to do with the body if you do kill it, etc. The second problem is far larger than how to trap a coon. They are one of the very easiest animals to trap using the above method.
p.s. This method also works for skunks and skunks also enter garages through cat doors.
Now if you trap a skunk.........
Good Luck!
williek