Add default app to open file - xperia zx2

[stavrich]

Just moved from blackberry to a shining xperia xz2 and android is very dark to me now.

I need to find a way to add my Mapfactor app as well in the default list of apps to open gpx files.

At this moment when I click on a gpx file ( via Files app) a get 6 apps to choose from but not Mapfactor. 

How can I add Mapfactor to the list of default apps.

xperia xz2

Android 9