How do I raise the feed dog in my Elna 5000, a machine I recently inherited.

I have a 7000 manual and from memory the 7000 was released a year after the 5000 and very similar. Look at top middle image below, for feed dog release at back of the sewing free arm.
At the back of the sewing free arm (remove the accessories tray) is a slide to lower the feed dogs, there is a little stub that you need to push to release it. Manual says "Drop the feed by pushing the slide (a), which is at the rear of the elevated sewing surface, to the left. To raise the feed dog again, press down the stud (b) and the feed dog will rise when you start sewing." You might need to wind the flywheel towards you half a turn to visually check they have come up.