That's a common place (the chin & neck area) for sheds to get stuck & need our help with; personally I get involved & make sure it comes off as soon as I see that the snake cannot do it on their own, because it only gets dried out & even more stuck.
Don't soak your snake in shallow water unless you're right there & have the time to make sure that part stays submerged. A better way is containing the snake for a few hours in a smaller tub with a thick & soaking wet terry towel -they MUST lay on the whole time- it will likely make the skin soft enough for either you or the snake to get it off. After a couple hours, give it a try, gently. You've most likely not been trying the other methods (wet pillowcase etc) for long enough. Once the skin is really dried on this way, it takes that much more effort & time to remove it. Don't leave it for the next shed. Be patient & persist. And next time, don't wait so long to help.