I hate to keep doing this to people, but if you are using Elementor Pro then this is a question you should be directing to either the developer of that plugin or to people that use Elementor because it is a question of how to use a value that ACF stores in that system.
The chances of someone that uses Elementor answering your question here are small. ACF is built primarily for developers that code templates themselves using PHP.
All I can really give you is that a relationship field stores an array of post IDs for the related posts.
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