Give the villager a Splash Potion of Healing or a Lingering Potion of Healing
Give the villager a Potion of Healing by using commands or mods if needed
Feed the villager a Golden Apple if the game version or mod allows it
Cure a zombie villager with a Splash Potion of Weakness and a Golden Apple
Let the villager rest and avoid further damage from mobs, fire, lava, or fall damage
Use commands to restore the villager’s health instantly if cheats are enabled