Try spraying WD 40 or another silicon spray. Chances, it won't work.

Then try a carburetor cleaner spray, they are absolutely terrific for melting away grease. However, there won't be any lubrication so you will have to spray a lube once it's free. I recommend Dura Lube spray.

To try to turn the freewheel, you may want to use a chainwhip, same as for a cassette. Of course your goal is not to remove it with the chainwhip, that's impossible, just to turn it.

All freewheels use a different tool, there are two dozen or more different sockets though there are only a few more common ones. Don't buy the tool unless you have a vise to use, it's impossible to remove without a vise. Go to a LBS and pay them $5 or $10 to remove.