Edit>preferences>Directories tab.
Click the button at the top ("DAZ|Studio content directories") and select Poser content directories from the list.
Click the Add button and use the dialogue that appears  to select the folder that holds the Runtime folder (it's the same one you'd pick to make an external Runtime in Poser).
Click Accept and the thing should appear in the Content palette, with a plain folder icon (the D|S content folders have a stylised S on them) and with the name of the actual folder that was selected.