Step 1: Navigate into a presentation that you are working on and then find the "+ Add" button on the top left of the screen. Click the "Add Slide from Presentation" section from this menu.

Step 2: Select which Chapter you want this new slide to be added to.

Step 3: Select the Presentation that you want to import a slide from and then navigate through that to find the specific one you are looking for.

Once hitting "Add Slides", the slides that you previously selected will be added into the presentation that you are working on.