How do change the x axis default from time to distance. I can do this on the connect webpage where there is a tab on the top right, but not on the
not on the app.
. 
I don't know, but let's be glad that we have this option now. Distance is only most important for the altitude profile, but for example, for heart rate, time dependence is better. And for the mutual comparison, it is probably not even technically appropriate to have different units set for different types of graphs.