Either you misunderstand the purpose of containers or I misunderstood your question.
Container itself is not an object, therefore there are no "container instances" and no container UIDs.
Containter is a way to logically link together several instances of different objects.
Only one instance of each object can be in a container.
For example: 1 Enemy sprite, 1 EnemyHealthBar sprite, 1 EnemyName text, 1 EnemySkills dictionary etc.
When you create an Enemy instance, all those other related objects will be created automatically.
When you destroy the Enemy, all instances of other objects from the container will be destroyed as well.
When one instance of any object is picked by an event, all other objects from the container are also picked automatically. So you can do things like this:
Bullet on collision with Enemy -> EnemyHealthBar set visible
Mouse On clicked EnemyName -> Enemy start flashing for 1 second
What objects are in your container? It's hard to tell from your screenshot.
If you need to link multiple instances of one object to 1 instance of another objects, containers will not work.
Say, if you want to group 1 HexCell, 7 Circles and 7 lines, you need to use instance variables.
Usually, you select a "parent" object (HexCell) and add an instance variable "HexCellUID" for all dependent objects (Circles and Lines). Then you can pick them:
Mouse On clicked HexCell
....Circle compare variable HexCellUID=HexCell.UID -> Circle set animation ...
Or the other way around:
Mouse On clicked Circle
....HexCell pick by unique ID = Circle.HexCellUID -> HexCell set animation frame to 1
(If you are using Pin behavior, you can refer to pinned objects with built-in expression PinnedUID)