The red dot indicates which Library is currently active.

Now click the + button down the bottom, and select your library on the external drive.

Make sure to select the PARENT folder of the new Runtime folder. The name of this parent folder will be the name of your new Library in Poser.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)