I wanted to know whether we can have a function in AGS to automatically resize the screen to the device's size?
If possible ,please reply.
As far as I know, you can't change screen resolution at game start, you need to pick how you want the screen to be displayed in computer by selecting it with winsetup.exe.
Might be possible to enforce it via script, but I have no idea how (nor do I want to enforce something that should be player's choice).
If you are using AGS 3.4.1, then you may also set default game scaling on the Default Setup page in the editor.