Diagnosis - Insert SIM Card To Access Network Services

I have a SM-G900H which took some water damage (toddler dropped it in the bathtub for a few seconds), despite that IP 67 rating.

It worked for a few seconds while I dried it and removed the battery. After a couple of hours drying out, I tried to turn it on. It gave a "low battery temperature" warning and a "SIM not reconized, rebooting" warning, and I instantly removed the battery (I supposed it was not completely dry yet) and shoved it in a rice bag for 48 hours.

I turned it on now. Battery is working fine, but the sim card is not recognized. I tested with another SIM card, so I know its the phone. In the place where the signal bars were shown, there is a "forbidden\no" sign.

I need some pointers on diagnosing which part took damage. My first idea would be to replace the whole motherboard, because as far as I have seen here the SIM connector is permanently soldered on it. I became doubtful when I saw some online ads for the SIM slot itself, not attached to the motherboard.

Is it possible that the slot is damaged? Is it possible to replace the slot alone?