In RMSS, there's no Healer spell for it, but the Cleric base list Life Mastery has "Heal Life Essence" spells which will do the trick.
Also, per RMSS Spell Law pg 241, it will recover on its own at a rate of 1/day when doing nothing but resting, 1/week if not traveling but still doing other things. Double in a place "soothing and sacred" to the character, +1d10/day in a place that is holy or consecrated.