Step1: Double-tap the slide that you want to comment on.
Step 2: Tap the New Comment button on the floating toolbar The New Comment button in PowerPoint for iPhone .
Step 3: The Comments pane appears full screen with a blank notation indicating your name and the date.
Step 4: Type your comment. Press Done to resize the Comments pane and make your slide visible again.
Step 5: You can use the toolbar to navigate backward and forward through comments.