From within an App Level Action Block, how do you modify the value of a field within an App State list?

I have an App State with a list of items that are of a custom data type. Within the data type, there is a text field that I want to search on to find a matching record. I then want to modify one of the other fields in that list item. I want to do this within an App Level Action Block

What might be the most efficient way to do this? I was hoping that a "Simple Search" would work, but it seems you can only do as an action on a widget. Is there a way to do this within an Action Block?

Thank in advance.