Calling EXE method from DLL

Please help me solve my problems by giving me some ideas or sample codes on how to call a method inside a WPF application (EXE) from a DLL (UserControl Library).

I have two WPF projects:
(1) MainProgram - WPF Application
(2) ViewsLibrary - WPF UserControl Library

Basically, the ViewsLibrary contains UserControls (e.g ViewA) which will be displayed in MainProgram as an MDI child.
The MainProgram receives message from the server, "Data Settings",  for the controls defined in ViewA.
In order for the ViewA to get/receive the Data Settings from MainProgram, ViewsLibrary needs to call a method inside the MainProgram (e.g MainProgram.SendDataSettings).
The controls in ViewA will be set upon receiving the Data Settings (ON / OFF / Alarm / Etc)..