Step 1. Open the required Team Channel in Teams online or Desktop App, and select the files tab.
Step 2. Click the filename to preview document.
Step 3. Click Edit at the top of the page, to open the document in editing mode.
Step 4. Click Review from the document Menu and click New Comment to begin commenting on the file. When complete, click Post to save comment.
Step 5. Other people viewing the document will see a speech bubble icon to indicate there are comments. To view comments click the speech bubble or select Review from the document Menu and click Show Comments.
Step 6. Click Close which auto-saves the document and returns to Teams window