how to active left mouse click

If you are trying to deteect it:

if (Mouse.Buttons == MouseButtons.Left)
    {
    ...
else if (Mouse.Buttons == MouseButtons.Right)
    {
    ...
    }

If you are trying to simulate a mouse button press, then you can use Button.PerformClick[^], but there is no direct way to force a right click in .NET - you would probably have to use PInvoke to send a mouse message to teh relevant control.

A better way would be to extract the code from the Click event handler and call it directly...