Logo image and Background image breaks SSL on login screen module

Hello, good day,
when I change the images on Logo image or Logo background in the login screen module, it breaks SSL in pages https://mysite/wp-login.php.

In the Media library the image URL are set to http and not to https:
Background image: http://mysite.com/wp-content/uploads/2017/09/Background-image.png
Logo image: http://mysite.com/wp-content/uploads/2017/09/Logo-Larfix.png

I think this is the problem, so I tried to change it with these plugins but with no success:
Better Search and Replace - https://wordpress.org/plugins/better-search-replace/
Search and Replace - https://wordpress.org/plugins/search-and-replace/

Also I found something that could work in this tutorial -
https://premium.wpmudev.org/forums/topic/custom-branding-breaking-ssl-on-page -
Where in-mn The Crimson Coder mention that modifying URL locations for these files to // instead of http:// could simply solve the problem.

The problem is that I don't even imagine how to modify URL from http:// to //.

When I remove the Logo and background images SSL works again with the default logo and background of wordpress.

When I say it breaks SSL I mean the green locker desappear in Chrome and in Firefox it shows a grey locker with an orange triangle, some description of this lock is here: https://support.mozilla.org/en-US/kb/mixed-content-blocking-firefox