How can I auto-select a parent record?

I am trying to setup a hierarchy where the parent is auto populated based on the child’s ID.

The hierarchy id is setup to show the relationship. example, ID 1.23.456 is the child of ID 1.23 which itself is the child of ID 1

So when creating a new record, when I input the ID 1.24 I have a TextFormula field that extracts the parent id: “1” I’d then like to auto-populate this into a Connection field.

I don’t see any way of doing that though: the Connection field Conditional Rules looks like you can only set it to the value of a related Connection field, not lookup based on the contents of a text field.

How can I do this?