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  1. Copy the cell with the comment, using Edit ▸ Copy or Ctrl+C,
  2. Select the target cell to which you wish to attach the comment,
  3. Right-click and choose Paste Special or go to Edit ▸ Paste Special or use Ctrl+⇧ Shift+V,
  4. In the Selection area, uncheck everything except Comments,
  5. In the Operations area, choose Add.