i can't find a reuqested image from another url

i have a problem with the SSL certificate, it shows some errors when i click inspect to see the errors, i find that i have a requested image (logo) that does not exist in PHP files.. i found it in HTML files, but i could not find it in PHP files

Mixed Content: The page at 'https://example.com/' was loaded over HTTPS, but requested an insecure image 'http://templates.smilethemes.com/insurance/img/icons/logo.png'. This content should also be served over HTTPS.