Water damaged Samsung Galaxy J6

Did the marker change color? Or, I mean, are you sure it's water damaged?
Just dropping it in water doesn't make it water damaged.

 

This is little solace to you now,

although I would have a good cheap back street repairer look at the motherboard, they may not charge

but if you plugged it in or turned it on straight after it's little swim you exacerbated the damage (made it worse even).

Everyone swears by the method they heard or tried, but I stick by another older gents long technical experience.

It's the (dried) tiny impurities in the water that cause the damage, ie shorting a tiny circuit board or something like that.

Rice may dry the phone quicker, or let it dry naturally (same difference) but a bath in Isopropyl Alcohol (other names) as close to 100% as you can get is the best way to clean the residue off the internals while the device has remained off.

Some immersions can be survivable if you're lucky, I dropped a new flagship Motorola X Style in a flushed toilet on holiday. I left it off for 2 hours and it was OK.
Your description doesn't bode well for any sort of recovery.
Have you backed up or accessed your Google account and Photos OK? Register for a Samsung account?

Good luck.