DANGER.... DO NOT SQUIRT WATER INTO IT.. there is a real risk it will get into the lungs and it will die.
Make a paste with chicken layer pellets or any chicken feed. Not too runny. Kind of like thick porridge. It will get all the moisture it needs from this mix.
Put this mixture into a plastic bag and cut a small hole in a corner. Put the pigeons beak into this hole and it will eat the mixture on its own until its crop is full.. Clean up the pigeon to keep it clean with a damp cloth.
Feed 3 - 4 times a day... always make sure crop is empty before feeding more food.. otherwise the old feed can go bad and it will get sick.
In the cage have a bowl of seed, pellets and also one with water. Every time you go to feed the bird.. encourage it to peck about at the feed by itself.. using you fingers like a beak to peck at the seed will encourage it.
Having hand raised many pigeon squabs I find this the best and most natural way to do it.