Select Method (IToolBar)
Selects the specified item in this menu. Do not invoke on a toolbar.
Remarks

Only visible items can be selected. You can use ShowDropdown(String) or ShowDropdown(Int32) to make the button visible.

C# Syntax
void Select( 
   string itemPath
)

Parameters

itemPath
The full path of the menu item is a list of menu button names separated by semicolons.