Wordpress - How to import CSV into Custom Post Type custom fields?
I used a plugin called Really Simple CSV Importer https://wordpress.org/plugins/really-simple-csv-importer/
If that link is dead, you can find it on github here: https://github.com/dansullyLT/rs-csv-importer
It populated my custom fields that I made in ACF.
Here is how I used it.
Download the sample CSV file the plugin dev offers you. You make each header row the field name and import through the WordPress > Tools > Import menu.
You have to include a column of post_id and post_name, but you can leave them blank. Make the post_type column the name of your custom field group and set the post_status. You may get some errors on import, but just read them carefully and you'll be able to correct them.
It worked great for all of my ACF except images. My images were a little complicated though.
There's a free version of this plugin that should do all the necessary work to import Custom Post Types from a CSV or Excel file.
The paid versions also allow you to import users and to better modify advanced custom fields associated with CPT's as well.