Series the first SSR with the secondary SSRV. This one I have is like a triac-diac combination. Jumper the out from the original to the in on the second one.. then go on to the heater coil with the wire originally on the first SSR. You are basically putting the SSRV inline.
You connect the two posts on the pot to create a variable resistor, inside it has a coil of wire and a brush that travels around inside it picking up off the round wound coil. IE the further you turn it, the lower resistance on the brush.. The less resistance on the pot the more current flows out of the cube.
I bought one too, not put it in my pot, it seems to actually "heat too fast and I was going to slow it down" by reducing the current flow through the heater coil.
Don't know how to scan to draw you a picture. I am on a Ubuntu Linux OS here.