I have a class from which I call a function ABC(string st) with a string argument.
ABC(string st)
The function is defined inside a Form class, Form1
Form
Form1
You can't invoke an event handler of another class - events encapsulate the idea of subscription and unsubscription for handlers, not invocation.
Which aspect of the ListView MouseClick event are you interested in? Would changing the selected item be enough, perhaps?