From the parks on the air FAQ page:
Q: How do I get a park added to the POTA database, or get park coordinates fixed etc…?
A: Over the last year we’ve updated the US database, and even though not every possible POTA entity can be activated, we are in pretty good shape, and will take a two year break before we will add more parks, unless it is a newly developed state/federally owned state or national park.
If you are seeking to add a new country, please write an e-mail to W3AAX via qrz.com. If you are wishing to add a park to an existing POTA country in the system, please go to our official site
https://parksontheair.com, Look up the appropriate country admin mapping representative, and contact them via their e-mail on QRZ.com, and please ask them. They are my voice from each country. We ONLY add state/provincial/prefecture etc. or national/federal level parks due to overhead. For park corrections in the U.S., please send them to the mapping coordinator on the main site. I get all corrections from them directly.