The memo is saved in a Word document.
Open it and click on the Review tab in the horizontal panel above.
Then click on Track Changes and Track Changes again.
Now begin editing the document. Every addition or comment that you make will make will pop up in red.
You do NOT have to rewrite the memo. You just need to mark corrections and put comments on why each sentence is correct (or not).
After you have completed this please save the Word document.