@areenamuzaffar Unfortunately, cell phone screens are actually pretty delicate and can be damaged by even a short fall, and it sounds like that's what's happened to yours. They really can't be repaired, so the only solution is to replace the screen. On your phone the approved/official way to do it is to replace the screen plus midframe assembly, meaning you'll be moving pretty much everything from your old phone to the new housing. Here's a guide showing you how.
[link|https://www.sosav.fr/guides/mobiles/samsung/galaxy-a30/ecran-complet|Complete screen (screen + chassis) Galaxy A30 repair - Free guide - SOSav.fr|new_window=true]
It's in French, but if you use it with the Chrome browser, the automatic translation makes it quite usable.
The other way to replace the screen is to just replace the AMOLED display without the frame, but that requires a different set of instructions. This video shows you the basics of how to do it; used in conjunction with the other guide I posted you should be able to get through it with no problem.
[link|https://www.youtube.com/watch?v=QEyNE89H3ZE|How to Replace the Samsung A30 Screen - Samsung A30 Screen Replacement - YouTube|new_window=true]
You can find replacement screens readily available; I usually start with places such as Amazon, eBay and AliExpress. This vendor carries both with and without frame versions so you can pick which one you prefer; there's only a couple dollars price difference.
[link|https://www.aliexpress.us/item/2255800852691923.html|100% OEM AMOLED For Samsung Galaxy A30 A30s LCD Touch Screen amoled Display Digitize Assembly Replacement Frame NO Dead Pixel|new_window=true]
Hope that answers your question, Areena. Let us know if you have questions.