Welcome to our community, TechySP
As you are new with RoboHelp, I'm going to provide
instructions for version 7.
Click View > Pods > Single Source Layouts
Double-click your layout and the properties dialog should
display
On that first screen should be a field labeled "Skin", where
you choose the skin to apply.
Note that if you are using the Section 508 option, you won't
be able to choose a skin.
Cheers... Rick