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 Fluid file you downloaded, unpack the two folders data and FluidForDaz to the My DAZ 3D Library folder
Switch to DAZ, right click and refresh the My DAZ 3D Library folder.
Fluid is now available in
MY DAZ 3D Library > Fluid For Daz