Hi
Sorry to hear that your iPhone isn’t in the best way!
What I would to here is turn it off as soon as you see this and take it to a repair shop and ask them to unplug the battery
The next part you can do
I would order some isopropyl alcohol and some screw drivers from ifixit (any of the kits with bits will do a grand job)along side a new screen
And dowse the board in the alcohol with the board out and with a soft toothbrush gently brush off any corrosion (it usually looks black white or blue)
oh and finally take it out the rice it doesn’t work ever ,if anything it just makes it worse due to all that starch from the rice witch does no one any thing good;-)
Hopefully this helps
If you need any help with anything just ask
Thanks:-)