Cross posting this solution from the Evernote Support forum.

If you are trying to work out how to find and replace inside Evernote (nb: this is a MAC only solution), here’s the best current solution (as Evernote doesn’t support it natively for some unknown reason).

  1. CMD-A the text of the note you want to edit.
  2. Right Click inside the note then Services ▹ New TextEdit Window Containing Selection”.
  3. Then in TextEdit “Edit ▹ Find ▹ Find & Replace”.
  4. Then copy all and paste back over selection in Evernote.