If you’ve ever wanted to backup or export your WordPress Customizer settings, there is a plugin for you. Customizer Export/Import by The Beaver Builder Team is a huge time saver. If you’re starting a new WordPress site and want to import the Customizer settings used on a previous site then this plugin is awesome. However, the most common situation we recommend Customizer Export/Import for is the late installation of a child theme.
Adding a Child Theme After You’ve Already Setup the Parent Theme
When installing a child theme, the theme slug changes, this means that all Customizer settings reset to default.
You may need to re-save your menu (Appearance > Menus, or Appearance > Customize > Menus) and theme options (including background and header images) after activating the child theme.
https://developer.wordpress.org/themes/advanced-topics/child-themes/
This is no problem if you’re installing a child theme at the start of your site’s development. However, if you’ve already set up menus, backgrounds and a long list of theme options, this is a big time waster. To avoid redoing all of your Customizer settings once the child theme has been activated, follow these easy steps:
1. Go to PluginsAdd New, search for, install and activate Customizer Export/Import.
2. With your parent theme activated (not the child theme) go to CustomizeExport/Import. Click the Export button which will download a .dat file to your desktop or downloads folder.
3. Assuming your child theme has already been installed, go to AppearanceThemes and activate it.
4. With your child theme activated, go to CustomizeExport/Import, under the Import heading, click the Choose File button, select the .dat file you downloaded in step two, enable the import images option and click Import.
Hopefully, you’ve found this helpful. If you have any questions or comments, please, feel free to post them below.