In the ppt interface, click the design option in the menu bar above, select the corresponding template according to your own needs, and click.

1. First of all, in the ppt interface, you can find the menu bar at the top of the page, as shown in the figure below.

2. Then click Design in the menu bar, as shown in the figure below.

3. Then, in the open options, select the template as needed, as shown in the figure below.

4. Click to replace all the background templates, as shown in the figure below, and that's it.