Three options: 1)With the help of healers in the cities like Doc Roberts in SHrouded Hills or Fawn in Quintarra 2)With bandages using heal skill (Jayna and Virgil can do it) 3)With major healing spell (third spell in White Necromancy colledge). Virgil, Dante, Perryman Smythe and Raven can do it if you ask them (chose the "I need healing" dialog option).