I would use WP All Import Pro with the ACF Add On https://www.wpallimport.com/
If I needed to do this without that plugin.
1) Create an image field
2) Use media_sideload_image() to create add the image https://developer.wordpress.org/reference/functions/media_sideload_image/. This returns an attachment ID.
3) update the ACF field with the attachment ID value https://www.advancedcustomfields.com/resources/update_field/
