It is U1 level but at Elisenhof. So instead of going into
Hertie Markthallen food hall, walk towards the underground entrance to Müller Drogerie. You are now in the basement of the Elisenhof, keep walking and Edeka is at the end on the righthand side.
But Hertie's nicer obviously (and not that much more expensive and a lot cleaner so a better choice if you're a bit picky).