It's horrible stuff... I had to throw away an outfit of my daughters because it didn't come up. Hopefully you can take the cover off the cushion. I did a search of the internet and this looks the most promising for you:
Step1-Rinse the stain under cool running water until the water runs completely clear.
Step 2-Place a paper towel under the stained area of the fabric.
Step 3-Soak the area with isopropyl alcohol using a cotton ball.
Step 4-Replace the paper towel as the stain is pushed out onto it by blotting with the cotton ball.
Step 5-Launder the fabric in hottest water possible with bleach or color safe bleach and dry as usual.
Good luck. Dry Erase is great for white boards but not for fabric!