Hi @ayush1269280
If two repair centres couldn't fix it, it is doubtful that you can but you can only try.
''The impurities in the water causes corrosion and provides circuit paths for the electricity which were not in the phone's operating design and could damage the components. The corrosion starts immediately and is ongoing until it is completely cleaned away''
''First ***do not try to charge or to turn on your phone*** and then ***remove the battery as soon as possible*** from the phone'' to minimize any further damage.
Then you need to dis-assemble the rest of the phone and clean ''all the affected parts'' using ***Isopropyl Alcohol 99%+*** (available at electronics parts stores) to remove all traces of corrosion and water. If possible do not use "rubbing alcohol" as in some cases this is only 70% IPA or less, can contain additives which may leave conductive residues and is not as effective. If you do have to use it check the label to verify the amount of IPA. The higher the percentage of IPA the better
Here is a link that describes what happens. [[Electronics Water Damage]]
As always with electronics, especially surface mounted pcb be gentle when handling and especially when brushing away the corrosion. You do not want to remove any components from the board. Remove the shields that may be covering some components as the water may have got in under there. The ends of any flex cables and their connectors need to be cleaned as well
Hopefully after you have done all this the phone ''might'' possibly work correctly again.
Here is a teardown [https://www.youtube.com/watch?v=RNC71ytnZlA|video] that will help.
If this doesn't work then there's not much else you can do. Hopefully you have previously backed up the phone before it was water damaged, to the cloud or a computer so that you can load your saved data into a new phone.
Remember to dispose of the water damaged phone responsibly. The environment will thank you for doing this