How to transfer data from one process to another?

Question

C++ / C#

Hello,
I have 2 applications, both written by me.
1 application is something like a launcher, it launches the second one and hangs as a process. Next, the first application on the server checks if there is an update. If there is an update, the 1st application should somehow correctly tell the 2nd application that it needs to end. Next, the first application downloads some files, and then launches 1 application again.
Both applications are written in c#, windows forms.
How can I implement something like this?
Now I'm doing this:

Process proc = new Process();
proc.StartInfo.FileName = "D:/dir/Programm.exe";
proc.Start();

proc.Kill();

Everything seems to be working, but the second program uses notifyIcon and if it is terminated like this, then the icon remains in the tray, when a new one is launched, then I already have 2 icons hanging in the tray. After hovering, one of them disappears. That is, in order for it to disappear, it is necessary to somehow make program 2 complete itself.
Thank you very much in advance!