On my 08 Endeavor PDQ the main access panel is the 4 big screws and it should just lift up and out .If you are trying to reach the back (fan/water pump) area that access panel only comes out after you remove the closet doors and the associated wood panel then find all the screws buried in the carpet. Can't remember how many there are.
Brian, Loretta & Daisy (Golden Retriever)
2008 HR Endeavor 40 PDQ , ISL 400
2010 Dodge Ram 1500 Toad