Been while but... it's simply a pair of a center push pin plastic trim rivets holding in place. Some come off easily enough w a quick firm downward pull on the shelf to release the plastic rivets. NOTE - I do NOT recommend this as can cause damage to the underside of dash if not done w/ an even swift pull.
Otherwise, reach up under dash and while using a mirror & flashlight to see, gently take a small flathead screwdriver and push the center pin of rivet back thru on each to release retention pressure on the 'fingers'. You can then remove pins completely w a pair of needles nose pliers in footwell. Or use a firm even downward pull on tray to release rivets and shelf entirely.
Good luck
