Add Setter to both edges, lay the decal onto the first flat side, wipe the decal top and bottom with Softer and it will usually bend down and lay onto the second edge on its own. Then you can wipe away all excess Softer and Setter.
I wanted to start trying panel lining and got this one. It is definitely not the right tool to use. The handle is very bulky and hard to maneuver around corners and small spaces. It does a great job making scribe lines on flat sheets of plastic if you are planning to add PLA plates for extra detail, but not panel lining.