I think I followed the video below, without the vinegar part. Just mix some baking soda with water to a paste, brush it on, wait half an hour and clean. Thick spot can take longer, but it generally works ok.
And I use that baking soda in the orange pack from the supermarket. Nothing fancy. Not as technical as @Douglas, but it works. I couldn’t find that cleaning soda anywhere was a key reason for me.
