A family of Microsoft presentation graphics products that offer tools for creating presentations and adding graphic effects like multimedia objects and special effects with text.
We can't give you specific steps, since you haven't posted what operating system or version of PowerPoint you're using. You can post a screen shot using the Insert image tool (circled below):
First, save a copy from the cloud to your computer, so you have a backup. Then try changing the slide size to see if PowerPoint automatic resizing will kick in again, hopefully with a better result. If that doesn't help repair the damage, you'll have to manually select all items and reset their size.