Navigate to settings and scroll down to find the default background settings for postcards and notecards.
Images uploaded here will be set automatically for any order submitted to this account/sub-account unless a different background image is specified.
Using the controls, upload your custom background browsing for the file you designed elsewhere or in Canva.
To clear a design, click on the red 'Clear Image' button.
Be sure to save any changes before leaving the page.