Put both lower parts together an secure with 2x Mx30 or a clamp.
Put topcover and core together and secure with M3x12
Make sure to get a snug fit.
Pour the heatresistant silicon into the lower part till it´s filled to abt 60-70%
Carefully insert the top part so the mold is fully closed.
Let it sit and dry.
Assemble the heater, heat it up and retighten it, when done remove the original cover and replace it by your new molded sock.
Mind the direction of the nozzle/thermistor when putting the sock on.
Finally mount the coolingblock to your hotend and attach the whole thing to your printer.
commercial resellers are welcome to ask for permission.