Apple Watch SE 1st Gen black screen, won't restart

First you need to remember the Water Lock function does not change the physical water resistance of your Apple Watch. A software setting can't change the physical condition of the water seals. All WL does is disable the screen's touch sensitivity so water splash can't cause unwanted operation of the watch. I would start by trying to make sure Water Lock has been turned off again - the current method on my Series 7 is to press and hold the Digital Crown for about 5-10 seconds, and you should hear some tones as it tries to blast water from the speaker. (If I remember correctly the original method was to turn the Crown several full turns). There is a slim chance this might also bring a reluctant screen back to life.

I also suggest putting the watch on charge and leaving it at least 1-2 hours, just to be sure you are not dealing with an unexpected low battery.

The other place I would look is the Watch app on your iPhone. This should give you a few clues whether the watch is alive, and maybe try forcing a new (different) default watch face. You could also look in the iPhone's Settings/Bluetooth entry to see if it appears as "Connected"

Rice as a drying agent is an urban legend and emergency method if nothing else is available. Think about it, your rice has been exposed to damp air and would have absorbed as much water as it wanted soon after the pack was opened (not very much unless it was boiling water).

For better drying suggest you try to get hold of some Silica Gel, either the prepackaged drying bags or simply a tub of crystals. You should be able to find it somewhere like Amazon or maybe even a local hardware supply. Reactivate by heating in your kitchen oven for an hour or two at about 240F/120C, often it has a moisture indicator which changes color. Silica gel will give you at least 10x better drying than even the best rice.