Hi Mustanggt,
First, welcome to ALR. The Chambers York is a nice parts set. Should be fun and will make up into a nice rifle.
A search here on ALR for "remove breechplug" will return many previous threads on the topic. Here's how I do it.
Is your barrel straight or swamped? I'm guessing swamped since it's in a Chambers York. Whether the barrel is straight or swamped you should use something to protect the surface of the barrel when you clamp it in your vice. I use thick sheet brass shims. For swamped barrels your shims need to match the barrel taper so the vice jaws contact the barrel evenly all the way across. I stack progressively shorter lengths of brass strips to make tapered shims. Superglue between the shims to hold them together. (there are many techniques and different tools for this. See above search)
You need a good sized, solidly mounted vise. Jaws should be about 4" wide. Clamp the barrel with the breech plug lug horizontal and the bottom of the lug facing you, so you are pushing down to loosen the plug. Leave about 5/8 to 3/4" of the breech end of the barrel sticking out past the jaws, so you don't compress the barrel threads on the plug threads. Tighten vise securely. There are many opinions and techniques on this step. See above search.
Get a big adjustable wrench (there are many opinions and different tools for this. See above search) and a piece of pipe that will slide over the wrench handle. Use a brass shim bent in a U shape to protect the plug. Mount the wrench but make sure the wrench jaws stop a little short of the top of the plug. Check your set up one last time to make darn sure you are set up to loosen, not tighten the plug. (Don’t ask me why that’s part of my routine.) Push down on the pipe. If the plug does not come loose, remove the pipe and get a big hammer (you are set to loosen, right?) Give the wrench handle a mighty blow.
If it’s still stuck, do a search on “breech plug stuck” for more ideas. Good luck and keep us posted on your build.
-Ron