Saving one-to-many relation on a record: how to handle the items that must be deleted?

Is there a best practice to handle a one-to-many relation in a record so that I can save and update the items selected from a multiple dropdown? 
(basically a use case where my object can have a list of related features, that can be changed).

In https://docs.appian.com/suite/help/26.6/Multiple_Dropdown_Component.html#usage-considerations, I see that I can use a foreach to settle my data.

But how do I say to Appian that it must remove the items that are not mentioned in the data I try to save?

From what I am able to do right now, it is necessary to remove the unwanted items from the relation before inserting the new ones.