If you would ever need to move an existing collection into another collection as a sub-collection you can do that and here’s how.
In my example I’ve got two different collections which I named it Marketing Team and Corporate Communications Group. Let’s just say in my world of "matrix" the organisation is now undergoing a organisational restructuring. I now have to make the Corporate Communications Group a sub-collection of the Marketing Group.
Select the target collection (in my case the Marketing Team) where I want the collection to sit under. Right-click and then select New>Link to Collection
In the browse collection screen select the collection that you would like to put as a sub-collection. Click OK.
Now you’ll have the Corporate Communications Group sitting under the Marketing Team collection.
You can now choose to leave the original Corporate Communications Group alone or remove the collection by simply deleting it from the list of collections. Happy trying!