You will first remove the plates found at the top of the fire box.
Do this by loosening the screws which will allow you push the plates up and they will then be able to come down. Then go to the cap and remove it.
Once removed you can push a 3” brush down the pipe. Do so until the pipe is clean. Place the plates back as found, and the cap as well. You can then scoop the junk out the stove and then use it once again.
You should check the pipe after 1 week of use and if still clean you can push it back another week. Keep doing so until you establish your rate of buildup and your cleaning schedule. Here
is a video showing how it can be done.