First dump all the oil, the crankcase is probably also filled with water. Remove the spark plug and try pulling the recoil. If it still doesn't move, spray a ton of penetrating oil (e.g. PB Blaster) into the cylinder through plug and hole and let it sit overnight. Next day, spray some more penetrating oil in the cylinder and try pulling it over. Will probably take some force to bust it loose. If it has freed up, great. Pull recoil several times with plug still out to get rid of most of the penetrating oil/remaining water/debris.
Fill with fresh oil. Install new plug+check for spark. Fill with gas and give it a shot. (I would clean out the carb quick first!!! Or might just want to buy a cheapo aftermarket carb on eBay once you know it isn't locked up)
Dump the oil out after ~<30mins of light use and refill with fresh.
I have 'rescued' a few similarly fated gx hondas like this with great success. Love these engines. Don't expect it to last or have the power of one that has properly maintained, but I'm sure it will run!