Maybe another member who has had your experience can offer some advice, but in the meantime I found this online -
https://www.whiteselectronics.com/device-care/troubleshooting/#q3
from the above link -
3. I own an underwater detector and was out hunting but didn’t get my lid on correctly. Now my detector is full of water. What should I do?
Water can be very damaging to any electronics. Salt water can damage a unit in just several days. First, remove the lid and the cover that holds the electronics. The cover can be taken off carefully with a small flat-head screwdriver. Flush the detector completely with water, especially if it has been exposed to salt water. Then dry as much of the unit as you can with a towel.!You can absorb the rest of the moisture by putting the control box in a plastic bag with uncooked rice.