Hi @denny83535
Did you check the LDI (liquid damage indicator) in the SIM card slot, (remove the SIM card tray) to see if the x marks on the white background of the indicator, became pink or red smudges across the indicator, you never mentioned if they were or not.
When you say that you "...disassembled the phone but I couldn't see any corrosion or signs of water.", did you disconnect the flex cables and check the connectors etc for any water or corrosion? Bit hard maybe but perhaps the water may have gotten under any shields as well, which wouldn't be seen.
If you didn't check either of the above, then perhaps it may be prudent to check and clean as necessary before replacing any parts.
''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 that 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 may help[[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 the ifixit [[Topic:Google Pixel 7a]] guide that may also help