WordPress Child Theme Help

Copy your customizations to the new style.css and functions.php files in your child theme before you update. Here is how to create a child theme.

The best way to make changes like this to a theme is to use a child theme, so your tweaks won’t be overwritten when updating the theme. Here are some guides in case you haven’t made one before:
https://codex.www.ads-software.com/Child_Themes
https://op111.net/53/

I find Child Theme Configurator very helpful:
https://www.ads-software.com/plugins/search.php?q=child+theme+configurator

OK, I have never used that.. copy your customizations to a text file then add them to your child theme.

Another possible option is to temporarily switch to a different theme altogether and then re-name the modified theme and then re-upload and activate an original copy of the modified theme and then use the files from the modified version to make the new Child Theme.