Encoder disc replacement

My name is Wayne, and I have an HP 130 that is no longer under warranty.
I was maintaining the inside of the printer and did something to give me the dreaded "3 symbol" display on the printer panel... (X-sheet/finger-button/paper jam). HP Support explained what it could be, so sure enough, I had accidently knocked the Encoder Disc off the gear so I removed the top and left panels, exposing the errant part and the other innards.
I am wondering what position this disc is reinstalled at and can I do it myself? Thanks for anyone who can help me! Wayne
HP said; "Please note that the Encoder Disc is not a customer replaceable part and it requires trained HP Technician to replace the Encoder Disc. I understand your concern and would request you to get the printer serviced through an authorized HP service provider.