"the npc should look for injured players or injured humanoids in the game.workspace.friendlies folder and move to them. if the healer is within 10 units of the target, it will heal 10 hp every 3 seconds"

-- server script 
local NPC = game.Workspace.NPC
local healAmount = 10
local healRadius = 10
local healInterval = 3
local pfs = game:GetService("PathfindingService")
local friendlies = game.Workspace.friendlies

local function heal(target)
    local humanoid = target:FindFirstChildWhichIsA('Humanoid')
    if humanoid and humanoid.Health < humanoid.MaxHealth then
        humanoid.Health = humanoid.Health + healAmount
    end
end

local function findInjured()
    for _, target in pairs(friendlies:GetChildren()) do
        local humanoid = target:FindFirstChildWhichIsA('Humanoid')
        if humanoid and humanoid.Health < humanoid.MaxHealth then
            return target
        end
    end
end

while true do
    local target = findInjured()
    if target then
        local path = pfs:CreatePath()
        path:ComputeAsync(NPC.HumanoidRootPart.Position, target.HumanoidRootPart.Position)

for _, waypoint in pairs(path:GetWaypoints()) do
            NPC.Humanoid:MoveTo(waypoint.Position)
            NPC.Humanoid.MoveToFinished:Wait()
        end

if (NPC.HumanoidRootPart.Position - target.HumanoidRootPart.Position).Magnitude <= healRadius then
            heal(target)
        end
    end
    wait(healInterval)
end