Library Location
Once Stacks are created and associated with the responses, you can easily edit or update them from the Library Location on the Response page.
To Update the Stack
After creating the response record,
Go to the Library Location section and click the Edit icon.
Click the dropdown and select a desired Stack.
A list of Stacks exist in the org appears in the dropdown and available to select.Click the Save icon.
The Library Location updated successfully message appears.
Once updated, the response can be seen under the recently selected Stack.

Click to enlarge
You can edit or update the chosen Stack only for the Active Response and Reviews from Projects > New Response Request.