Can I make screen(opening page) before "Screen 1"?
Unfortunately, you can't rename screens. However, we added the ability in a recent release to copy and paste components from one screen to another. To do so, select the first screen, press Ctrl+C (Cmd+C on macOS) to copy the screen. Create a new screen and press Ctrl+V (Cmd+V on macOS) to paste the contents. Then you can go back to the original screen and remove its contents.
Another option is to open a splash screen from Screen1 in the when Screen1.Initialize event.
See this example :
On it's own, that does nothing useful Salman.
The Object of the exercise is to retain the current Screen1, so opening a splash screen within it (a Vertical Arrangement), as mentioned by Evan, is the best solution.
I have (finally) put an example up on my website - I actually have a few variations but no time at the moment to update the site.
https://www.professorcad.co.uk/appinventorsnippets#SplashScreens
Here you will find code that uses a Vertical Arrangement to contain the Splash Image, and a Vertical Scroll Arrangement that contains Screen1's components.
In an ideal world, for all but the most simple Apps, we should all be making Apps using Virtual Screens - they use less code and are generally easier to manage as a Project. Switch-Screen Issues do not exist. They also make more efficient APK's.