How to assign an owner (parent) to existing Value List Items in M-Files

Hello,
We have an implementation challenge and are trying to understand whether it can be solved through the M-Files API.

We have two value lists: List 1 and List 2.
Over time, both lists accumulated many items. Recently we were asked to restructure them so that List 1 becomes the parent value list of List 2.

After setting up the relationship between the lists, all existing items in List 2 naturally have no parent, since they were created before the hierarchy existed.

We are trying to find a practical way to assign an existing item from List 1 as the parent/owner of an existing item in List 2, but could not find any UI-based solution.

In code, I noticed the fields ParentID and OwnerID on ValueListItem, so I tried something like:

However, these fields do not actually update in the vault.

My question:
Is it possible to assign a parent (OwnerValueList / OwnerItem) to existing value list items using the M-Files API?
If so, what is the correct way to do it?
Should this be done using ValueListItemInfoAdmin instead of ValueListItem, and does anyone have an example?

Environment:

• M-Files VAF (AfterCheckInChangesFinalize event)

Any guidance or examples would be greatly appreciated.