@sajidtalati you said you cleaned any corrosion "from the connection ports" but you are not saying if you cleaned all the boards. You do need to remove the EMI shields from your boards. If you do not remove the shields, you are not cleaning the board.
Once you got the shields and the boards removed, clean your parts some more. For a proper cleaning, use this guide. It was written for an Apple iPhone 3G but it is still pertinent to your phone as well. I can not stress the importance of a good cleaning enough, so do it over and over while replacing the alcohol after each cleaning.
In your case, I would probably not clean the sub_board (charging board) but I would replace it. The boards are relatively inexpensive and by replacing it, you eliminate any issues with that. Do not forget to replace the battery. This is a must and not an option. It will fail if you do not take care of it now.
After that, reassemble your phone and re-evaluate. For as long as you have not cleaned your board properly and replaced the battery, everything is just a guess. Keep in mind that water damage is the hardest to troubleshoot and to repair. It does not matter if is was exposed for 2 seconds or 2 hours, what matters is where the water (particulates) did the damage.
You also need to keep in mind that it is possible that your display has been shorted out. You may have to replace the display assembly as well.
Huawei Y7 2019 Charging Board Replacement
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