WORDPRESS/WOOCOMMERCE - Pass user custom fields to order meta

Relevant Setup Details:
WP site on Avada child theme, running WooCommerce, ACF.

Challenge:
We have a WooCommerce site in which users can add event delegates to their user account. These are ACF repeater fields containing 4 fields per delegate. Each user can have multiple delegates and associated fields.

Users purchase event products (set up as WooCommerce variable products - not using an event management plugin). We need the user to be able to specify which delegates are related to which items in an order. For example, they may have 5 delegates on account, but only buy two tickets, so we need to pass which two delegates are related to that order (or that item in the order).

Option to confirm user can be made at add-to-cart stage and changed on cart page and/or checkout review stage.

Will run through current site set up to give a full view of current configuration and desired outcome.