Problem: I have two custom post types in a one-to-many post relationship. Province is the parent (one) and District is the child (many). I would like to generate an export CSV that includes each District title and its parent Province title.

Solution: Go to wp-admin > All Export > New Export. The first step is to choose a specific post type, and choose District as that post type. Then click "customize export file" to move on to the next step. Usually ID, Title and Content are already in place in the builder. You can drag the ID and Content blocks out of the box since you don't want to include those items.

Next click "Add Field" below the builder area to add a new custom column for the Province Title. Choose the option to select a field to export, and select the ID field. You may need to reset the column name information after choosing the ID field. Check the checkbox to export a value from a PHP function, type prov_parent_title in the function name field, and paste this function in the function editor to define the custom prov_parent_title function:

[php]

Relevant Documentation:
https://toolset.com/forums/topic/export-custom-post-type-data-and-related-repeatable-field-group-data/