At least I think that is what it is
The arm is the darker part and the other is the seat
Fill a bucket about 1/3 full with warm water. Mix in a squirt of Dawn dishwashing liquid and apx. 2 heaping tablespoons of OxiClean. Dip soft brush into water mixture and gently brush fabric, working out stains. You will want to do this to the entire seat (or area you are working on). Lastly, blot out as much water as you can with an old towel and brush area all in the same direction. Allow to dry completely. Hope this is helpful. :)
Here's a good article on cleaning microfiber: https://www.onegoodthingbyjillee.com/clean-your-microfiber-couch-safe-easy-way/
Microfiber is polyester. Have you tried an upholstery cleaner?
The light circle looking area, on the right looks like the color has pulled out of it?
Spritz with rubbing alcohol and blot, do not scrub.
I clean mine with chlorox wipes and then go over that with a damp towel. Looks great.