I've been trying to export a model to the game "transport fever" and I keep getting this error each time I try and export:
You should read error messages more carefully, it says the mesh has NGons not "rignors"
NGons are polygons whith N sides, that means your model that has more than four sides.
NGons are generally considered a bad modelling practice in general, and should be avoided for a multitude of reasons; and in many applications and file formats they are not even supported, so sounds like you have some cleanup to do.
Open all your meshes in Edit Mode and look for faces with more than 4 sides and remodel them so you have a proper quad dominant topology.
One quick (but unadvised) way to fix it it to blindly triangulate your mesh, by selecting all your faces in Edit Mode and pressing Ctrl+T.
Other less ill advised method is to transform all into quads with Alt+J.
Lastly the recommended method is to properly retopologise your meshes using a carefully planned topology that will ease future editing