Create a new rule named Doctor. Set its text to the following:

If a villager is the Doctor, e may secretly tell the mayor of a villager who is their target. If their target would otherwise have been killed by a werewolf attack, the doctor instead saves the villager from death. If the town has no doctor, the mayor shall randomly select one living, non-werewolf, non-night watchman villager to be the doctor, and secretly inform the villager of their doctor status.

In the rule Night Watchman, change the text

If there is currently no Night Watchman, the Mayor shall randomly select one Living, non-Werewolf Villager, and secretly notify that villager of their new status

to

If there is currently no Night Watchman, the Mayor shall randomly select one Living, non-Werewolf, non-doctor Villager, and secretly notify that villager of their new status