Unlike Word and PowerPoint, Excel doesn’t automatically highlight misspelled words for you.
So you’ll need to run a spell check manually.
There are 2 ways to do that.
The first is to hit F7 on your keyboard. That brings up the Spelling window:
This is just like the spell-check window in every other Microsoft Office app. At the top of the window, you’ll see the word that Excel has flagged.
Below that, it gives you options to replace it with. All you need to do is select one of the options and hit Change. If you want to replace all the instances of that word, you can click Change All.
If Excel has flagged this word in error, you can tell it to Ignore Once, in which case it will flag that word next time you check the spelling of your document, or Ignore All to never see it brought up again.
To add the word to the custom dictionary so it doesn’t get flagged again in any document, hit Add to Dictionary.