Is the printer still working ? did you open the printer cover at any location for some reason ?
Do you somewhere see a hole, an opening in the cover where that part would fit - e.g. a window for a display ? If not I just would leave it as it is, just use a piece of tape and stick it to the back of the printer, you may find that location later.
You have black spotches at the edge of the paper - can you check how the cleaning unit looks - is there any pigment smear ? You can disengage the printhead by powering off and on the unit and pulling the power cable when the printhead starts moving.
Are you trying to print on CD ? I don't think that would work, you cannot raise the platen gap that much.