I created a coordinate system through the Reference Geometry tool. I'll call this Coordinate System 1, which has x, y, and z-axes. The Global Coordinate System has X, Y, and Z axes. 

I want to create Reference Axes along the axes in this Coordinate System 1. So, I hover above each component of Coordinate System 1 to select the x, y, and z-axes to create the corresponding Reference Axes.

I'm able to do