changing over from outlet valve Caroma concord 6-3 to caroma quiet flow?

On the box it states easy installation but inside it comes with an 8 page instruction on A4 size paper.The Concord is not listed in the Reference chart and it does not fit .The Quietflow has a thread at the bottom and there is no where to screw it into in the Concord6-3.The plumber shop I purchased it from said this is the correct model.