How do I find the numbers for filling in the details of Insteon item?

So I am not sure if F00.00.19 is correct. I followed this github repo and am not sure if that makes any sense? How should I find this number? I found the other number 27.28.88 at the back of insteon dimmer.
Dimmer iot_insteaon_dimmer "IoT Smart Home Light" {insteonplm="27.28.88:F00.00.19#dimmer"}

On that page, it says and I have a LampLinc dimmer too:
2457D2 LampLinc Dimmer F00.00.19 Jonathan Huizingh

My other question is why the Insteon dimmer item doesn’t show in the sitemap?
I have this specifically for Insteon dimmer but nothing shows in the sitemap except the already hue lamp I’ve defined.
pi@raspberrypi:/opt/openhab/configurations/items $ vi iotpi.items

Switch iot_hue_switch1   "IoT Lab Light Bulb"   (Switching) {hue="1"}
Color iot_hue_color1     "IoT Lab Light Bulb"   (Colorize)  {hue="1; colorTemperature; 30"}
Dimmer iot_insteaon_dimmer "IoT Smart Home Light" {insteonplm="27.28.88:F00.00.19#dimmer"}

I have Insteon homekit hub model 2245-222 and I am running OpenHAB on Raspbian Jessie on Raspberry Pi 3.