Send Message To A Program

Hi All

I have received a reply from PCSoft about getting App A to get App B to be active. The answer is cryptic and I have no idea where to start"

"You may try to send a Windows message to the program"

That makes sense but.....

1. How do I get the handle of the window of App B if App A and App B are the exact same app but different instances?

2. What is the message that I am going to send to the app to get it to be active?

Getting there but very slowly.

Cheers
Andre