Hello @Hlin0,
If you're the host wanting to remove someone from your co-host list and the instructions in the article below don't work for you then contact Airbnb support.
Sometimes Airbnb's help instructions aren't kept up to date when they make changes to the website.
I can see that the instructions on removing yourself as a co-host from someone else's listing are now wrong.
How do I remove a co-host?
To contact Airbnb support click on "Help" and then on "Visit the help Centre" and then on "Contact us". That page has links for a phone number and sending a message.
You can also type "contact airbnb" in the "Search the community" box on these forum pages where you asked your question.
Click on the "Contact Airbnb: A Community Help Guide [UPDATED]" link. You may have to scroll down a bit in the list to see it.
Steve.