where can I find the installer toenable me to down load "hea rts of stone" for the PC

Go and click on the little Gear which symbolises settings in the GOG application(bottom left; it's definitely there). Then
a new tab pops up. There, it shows you where all add-ons and extras from GOG are downloaded to. Go to that place
in Documents, and double click on the hearts of stone application. I think that should help you to install HoTS.