Healing NPC can help us in events like Radiation Rumble or Project Paradise.
That's why you should have Friendly Fire perk.
This perk card let us heal teammates by hitting them with your flame weapon.
You need at least 3 charisma and level 48 to equip this card.
Every level of this card regenerates more health.
Basically if we need flame weapon then why no one is using Flamer? Well, Flamer is not working with this card. Only flamer's bash attack works but it's way too slow that's why we are using other weapons like Shishekab.
Shishekab is the best weapon to heal NPCs
Shishekab's attack is much faster than bash with Flamer, especially if you have 40% swing speed on it.
We can also use Martial Artist perk but game can't even sometimes detect you healing mobs with 40% swing speed, that's why Martial Artist is serious overkill.
You can also install Extra Flame Jets modification on your kebab, it will increase damage.
How to heal NPC?
Simply equip a Friendly Fire perk card.
Then use your Shishkebab to attack your teammate NPC - this is how you heal them.