All you need to do is head up the stairs where you will see the Blood of Lathander. You shouldn’t, however, reach for the mace just yet, as you need to do something beforehand. Indeed ...

Once per Long Rest, when your hit points are reduced to 0, you regain 2~12 hit points. Allies within 9m also regain 1~6 hit points. Lathander's Light Sheds holy light in a 6m radius. In combat ...