NOTE: This will only work while you're in a call (You can make a meeting and just join it yourself)
Step by Step instructions below this gif!

Click the 3 dots to get the menu up within a meeting and click on "Background Settings"

At the top of "Background Settings" hit "Add New"
Navigate to the picture you want and click open (or double click the picture)

Scroll down to the office picture and click on it then click on apply.