Hope these ideas help.
I would vaccum it.
This link should help:
China bristle brushes work really well because they have stiff bristles. They are also dirt cheap and are available at Walmart, home improvement centers, and online.
I recently came across this post about cleaning air conditioner coils. I hope it helps. https://www.familyhandyman.com/heating-cooling/air-conditioner-repair/how-to-clean-a-room-air-conditioner/
I found this article very helpful because they describe properly about portable air conditioner coil.
Hi! I use my vacuum, compressed air, microfiber cloths and an old paintbrush. If you can't reach something, try one of those long brushes made for dryers. Always make sure you have unplugged the unit, first.
Thanks a lot.
Here is a video tutorial for you: https://www.youtube.com/watch?v=XIwMIMKq7Ec
Before you begin, unplug it.
I have used a combination of an old paint brush (cheap one from the second hand store) and a vacuum cleaner with the bristle attachment. The brush will loosen and get in the cracks, the vacuum will complete the job. That does the trick for us. I try to not loosen up anything that looks like black mold, for that I spray white vinegar to kill it, let dry and then work on it.
There is some good information here:
Carrier has a good post https://www.carrier.com/residential/en/us/products/air-conditioners/air-conditioner-coil-cleaning/
Thanks a lot everyone for the awesome information.