There are two ways to start Ansys Polymat from Ansys Polyman:
Select a material data file in the relevant simulation branch of the project tree, and then select the Programs > Others > Polymat menu item.
Programs → Others → Polymat
Select a material data file in the relevant simulation branch of the project tree, and then type Ctrl-M.
Ansys Polymat will start and open the selected material data file.