Loading mixed (insecure) display content – How should I fix this?

How should I fix this? I have the yellow exclamation point. The last time i saw it I think I understood it has something to do with a page display function. The theme guys fixed it for me so I'm not sure what to do. Bug console says: JQMIGRATE: Migrate is installed, version 1.4.1 Loading mixed (insecure) display content “http://www.twenty-spot.com/wp-content/uploads/2019/04/artefact-dots-memory-1.jpg” on a secure page. There's a couple more numbers, not sure what they pertain to though... Thanks