yes you are able to do so in a Microflow.
You can use the "change object” action and select the Object you want to change. This will then allow you to select a member of that Object, being an association or an attribute. After that you can choose between set/add/remove, in your example you could SET the value to empty or REMOVE a specific object from the association.
Hi, depending on the association in a Change Object action in you Microflow you should at least be able to set the association as empty or remove an association