How to Duplicate Slides in PowerPoint
Windows : Select a slide in the sidebar and and press Ctrl + D. Mac : Select a slide in the sidebar and press ⌘ Command + D.
Open your PowerPoint presentation if it isn't already open. To do so, either double-click the presentation file, or open PowerPoint and select the file's name from the left side of the window. Find the slide you wish to duplicate in the sidebar. The column of slides in the left pane of the PowerPoint window displays all slides in your PowerPoint presentation. Right-click your slide's icon in the sidebar. The sidebar is on the left-hand side of the PowerPoint window. Right-clicking one of the slide icons here will invoke a drop-down menu. Click Duplicate Slide. It's near the middle of the drop-down menu. The copied slide will appear immediately after the original slide. If you want to move the duplicate, you can click and drag it up or down the slide column to change its order in the presentation. Double-click your PowerPoint presentation if it isn't open. Doing so will open the presentation in your Mac's PowerPoint program. Find the slide you wish to duplicate in the sidebar. The column of slides on the left pane in the PowerPoint window displays all slides in your PowerPoint presentation. Click a slide's icon in the sidebar. This should be the slide you want to duplicate. Clicking this slide will select it. Click your Mac's Insert menu item. It's in the top-left side of your Mac's menu bar. Clicking it will invoke a drop-down menu. Click Duplicate Slide. This option is in the drop-down menu. Clicking it will create a copy of your selected slide and insert it directly after the selected slide in the presentation. You can click and drag the slide's icon up or down in the sidebar to reposition it. 
Open your PowerPoint presentation if it isn't already open. Find the slide you wish to duplicate in the sidebar. Right-click your slide's icon in the sidebar. Click Duplicate Slide. Double-click your PowerPoint presentation if it isn't open. Find the slide you wish to duplicate in the sidebar. Click a slide's icon in the sidebar. Click your Mac's Insert menu item. Click Duplicate Slide. 