Which part? The shiny piece that is at an angle is intended to let you lock up the arms when you aren't using the deck.
What happens if you lower the rear wheels to their lowest setting? It looks like your front corner wheels are on their lowest setting and with the back ones halfway up, they might be holding the back up.
Before you do that though, can you spin the blade on the discharge side to it is pointing straight forward/back and measure the distance from the concrete floor to the tips of the blade?
Aaron Z