As a Bonus Action, you can heal your own wounds. Roll one of your unexpended Hit Point Dice and regain a number of Hit Points equal to the roll's total plus your Constitution modifier. This die is then expended.
As you gain Martyr levels, you can expend more dice each time you use this feature, adding your Constitution modifier to each Hit Point Die you roll. The number of Hit Point Dice you can expend equals half your Martyr level, round down.