How do I make a script run when someone resets their character?

I would recommend using the .Died event as Bucwheed suggested.

local player = game.Players.LocalPlayer
repeat wait() until player.Character
local hum = player.Character:WaitForChild("Humanoid")

hum.Died:connect(function()
    -- insert whatever you want in here
end)

Use characteradded.. something like this.

giveGun = function()
    print('Hi!')
end
game.Players.PlayerAdded:connect(function(p)
    function a(player, id) --So you don't have to redefine a variable all the time
        return game:GetService("GamePassService"):PlayerHasPass(player, id) -- checks if the player has your gamepass
    end
    p.CharacterAdded:connect(function(c) -- this is the part that you needed help with. everytime the character spawns, it continues to the next code block
        if a(p, 364868976) then --no, i just grabbed a id from a random gamepass I looked at
            giveGun() --gives you the gun
        else 
            print('no wep for u :(')
        end
    end)
end)

Humanoid.Died probably wouldn't work because everytime you die, the localscript in StarterPack reloads. Therefore, completely ruining the purpose of using .Died in the first place.

BUT, .Died can also be used to make you drop all weapons that you had on death. Oh, yeah. If you use p.Character:FindFirstChildOfClass("Humanoid").Died in a serverscript, that could work too.. probably.

if I missed something, tell me instead of flaming me. Thanks.