I click on Exclude 3rd party and move any 3rd party airports that are in the Enabled section to the Disabled section.
When you click on Exclude 3rd party, all 3rd party sceneries that will be recognized as such (their package name must conform to the official naming convention
developer-airport-icao-airportname) will be automatically moved to the Disabled list.
Those that have non-confirming package names, so they won't be automatically recognized as 3rd party airports, should be added manually to the Disabled list, by typing their code in the search area on the top right, and moved to the Disabled list with the button with the right arrow.