There’s no easy way that I know of. But here is how I would do it.
Save a copy of your style.css file to a text file on your local PC. Call it something like style-new.css or style-indexvision.css.
Go to the Zerif Lite Subversion Repository and copy/download a copy of the style.css from the version that corresponds to the one you have currently installed.
Use a text editor like Notepad++ to do a comparison. Many full-featured text editors have a file comparison function that can be used to compare, and show the difference, between two files. For Notepad++, you have to go to through the Plugins menu to first install the Compare plugin. Alternately, if you are familiar with Microsoft Word, Word has a revision tracking feature that will mark up the difference between two documents.
Whatever differences you see, you want to use to create your child theme’s style.css file.
Now, some people just copy the entire modified style.css file into the child theme folder without going through the hassle of looking for the differences. That’s usually fairly safe, you just might not get any CSS corrections that may have been done with a theme upgrade (but CSS corrections are fairly rare).
For the other .PHP files, if you don’t remember which files you’ve changed, I would use either an FTP client like FileZilla, or your host’s Control Panel, and navigate to the theme’s folder (/wp-content/themes/zerif-lite). Then sort the files by date in descending order, and you should be able to tell which files were modified. All of the original files should have the same date (the date when the file was loaded or installed). All of the files that you modified should have a later date. Then download and/or copy those files into your child theme’s folder.
