How do I access list values in flow

I am struggling a bit with accessing individual values in list that is returned by APEX code into the flow.

public class DynamicField {
    @InvocableVariable
    public String key;

    @InvocableVariable
    public String value;

    public DynamicField(String key, String value) {
        this.key = key;
        this.value = value;
    }
}

I return List<List> and I am able to loop through and print each list. The keys and values are there and I am able to show them in form:

{
  "key": "value"
}

But in the flow, I would like to assign the value to a specific variable. And so far I am able to assign only the list, not the value.

Any idea how to do it?

Thanks.