How to fly to an uncharted airport?
I know nothing of X-plane, but I fly gliders in real life and often land in fields and "uncharted" airports.  Uncharted does not mean the airport does not exist. However, you do need some idea of where it is, GPS coordinates, or some fix from a known point.  Even a general description of its location can get you close enough to find it.  I have often used "Google Earth" to pinpoint a potential landing area and once I find it there, I have what I need to navigate to it.  I check the date of the GE photography some are several years old and things could have changed that make the field unsuitable.
GE also has tools that you can use to measure the length and width of the "runway" and its orientation.  I look for obstacles that might interfere with my approach.  I also check to see if it is fenced because that can complicate getting my glider out of the field.