Hello Anand,
So to block the ".scr" file, it cannot be done using a simple file filter profile, because the file types that appear are the only ones supported.
The solution to block ".scr" files or other types you need, is to use the DLP Filter.
This link will guide you to achieve your objective:
https://docs.fortinet.com/document/fortigate/6.4.8/administration-guide/153498/data-leak-prevention
Go to: Basic DLP Filter Types link, on the page to get how to do it using the CLI.
Hope this helps to solve your problem.