Outside the United States, the airport data is primarily based on openAIP.net . Any change there will find it's way into Avia Weather the following week with the next in-app AIP update (scheduled every 1st and 16th of a month). If you encounter any error, we would kindly like to ask you to join openAIP.net and help update the data there to keep it up to date for everyone.
For the United States the airport data is provided by the FAA. If you encounter any errors there, please contact them.
In any case, keep in mind that Avia Weather is not a certified software and that you should always double check the data with an official source before flying.