You can update field values with update_field.
How are you values saved in the ACF Field group? You need to match your code with the Return format in the field.
What happend if your change “j F Y” to “Ymd”?
For (large) CSV imports, I almost always use the WP All Import plugin with the ACF Addon. With that, you can easily create imports for custom fields and auto-populate fields by a field of your choice.
Isn’t it easier to use the built-in WordPress categories for your custom post type? That way you could create archives a lot easier.
If you want to repeat field, you can use the Repeater field. For each of the repeaters you can add custom fields such as name, phone number.
Does that answer your question?
I’m not sure if I understand you correctly. I created a checkbox field on the backend and adding your code to a single.php file. When selecting a value in the backend, it correctly shows my selected value.
If I understand your question correctly, you want to retrieve the chosen values for usage in your template files.
Here’s information on how to get values from other posts:
https://www.advancedcustomfields.com/resources/how-to-get-values-from-another-post/