Launch DAZ Studio
In the content library tab, right-click on My DAZ 3D Library.
Select "Browse to folder location".
The My DAZ 3D Library folder should open...
In the playground file you downloaded, unpack the three folders data, Props, and Runtime to the folder My DAZ 3D Library
Switch to DAZ, refresh the My DAZ 3D Library folder.
Your playground prop is now available in
MY DAZ 3D Library > Props