In the Zoom app, click your profile in the top right corner, and click Settings.
On the menu to the left, click Virtual Background.
You'll see a few default background options provided by Zoom, including an outer space scene or blades of grass. You can choose one of those by clicking on it, and it will automatically change your screen as well. There's also an option for if you have a green screen and want to use that.
If you want to upload a photo to use as your background, on the same Virtual Background Page, click the + icon next to where it says Choose Virtual Background. A box will pop up allowing you to upload a photo from your computer. Click on the one you want, and it will appear alongside the other pictures as an option for you to choose from.
To get rid of any photos you upload, tap the X in their top left corner.
Click Download to save the image you want.
Add the image to the following folder in your file explorer: %APPDATA%\Microsoft\Teams\Backgrounds
Or if you do not have the Backgrounds folder you can manually create a Backgrounds folder and add the image.