Finally Airbnb gave the correct guide; i've tried it and it worked!
It has to be done from the Host account. The steps: (i tried this on laptop, it may be diff on mobile app):
1. Login to the host' Airbnb account.
2. Go to Your Listing.
3. Then click on the button that says "Calendar and more".
4. On the menu that appears on the left side of the page, look for "Co-hosts" and click on it
5. You scroll down from the page and you will find in blue letters "Turn off shared earnings"
Once you turn it off, it will clear out and once turned back on it will give The host the opportunity to change the percentage