Auto create connections with a function?

[fine-G]

How can I create connection with an action on creating and updating a post?

My CPT posts that should connected to an "parent" CPT have already an ACF-Realtionship connection between these posts. To make this connection double is not userfriendly.

Is there an action I can call on the create and edit post hooks?
My idea is to auto-create the connection by saving the child post.