There might be some water at the volume up key hence its not responding. Or responding weirdly. Turn it off and keep it in rice for few hours. Rice can absorb moisture. Try if this helps.
it might be shorting around the vol up key and causing circuit current to activate screenshot instead of increasing volume use blow dry or vacuum to blow air and dry the switch keep it idle for drying for some time
We at Samsung understand the situation as phone is one of the essential part of our day to day activity.
Further as mentioned that your device has fallen in water surface, hence this might be the reason of the issue you are experiencing in your device. We would request you to please visit the nearest service center for physical inspection of the device. However, post physical inspection at service center we will be able to confirm the same
