If I understand you correctly, when you start this Rainmeter program, the window that opens is not seen because it opens where the second display used to be.
If this is correct, you should be able to go into your graphics control panel and remove the secondary display from your system's configuration. This should make all programs open on the only available display.
If that does not work, while the program window may open on the secondary display, there should still be an icon in the task bar for it.
Mouse-over the icon, but do not click.
After about 1 second, the program preview window should appear. Move the mouse cursor over the preview window.
Right-Mouse-Click on the preview window and select Move.
Tap either the left or right arrow key on your keyboard.
You should now be able to move the window either left or right with the mouse (without clicking) until it appears on your display.
Once the window appears where you want it on your display, Left-Mouse-Click to set it in place.
From now on, when you start the program, it will appear in this new location.
-Wolf sends