From what I have read, there is no way to convert an account set up personally to a LLC. Some posts suggest there is no difference in your setup of the account.
I reached out to customer service and they did not know what a LLC was.
I'm not surprised customer service don't know what an LLC is, as this relates to how you set up your business and they won't be familiar with the terms used in each country.
If you look on Airbnb Help though it shows you how to set up your profile as a company account.