Definitely do not use water on the cut edge. Any drips will spread the bacteria further.
Cut, then use the cinnamon if you like, then keep the plant drier than usual. Don't water for a week. If you go a week and the rot has not reappeared, take a paper towel & isopropyl alcohol (or peroxide), wipe down the remainder of the leaf. Take a new paper towel & more alcohol, wipe the other leaves.
Wait another few days. If there is no returning infection, carefully water jus the roots. I would do the alcohol wipe down again.
If at any point the rot reappears, cut the entire leaf off, be sure to use a sterile blade.
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