How to find a file/line on WP site

I have installed flexible SSL option from cloudflare on my website. I have installed the cloudflare plugin for wordpress and also cloudflare flexible SSL plugin. I have also made the changes in the page rule to redirect the site to HTTPS. However I am still getting a mixed content error. I checked for the error on whynopadlock website and got this test result.
A file with an insecure url of “http://secureservercdn.net/160.153.138..myftpupload.com/wp-content/themes/astra/assets/fonts f” was loaded on line: 677 of https:// (domain name). How to resolve this. I am very new to website development and have no coding knowledge. How can i find line 677 mentioned in the test result.

That’s a question best asked in the Astra support forum or Stack Overflow.