Near the bottom of the Layers drawer - Enabled Actions popup menu -
choose "Select Others" --- the "others" means other layers. In this
case you can select anything that is visible on the drawing.
Flatten - you really almost never need to Flatten with EazyDraw,
everything is always "easier" than that. The video tutorial on Layers
covers this and has a bit of a warning about "flatten" is not usually
needed.