How can make a different running animation when I carry a specific weapon?

I'm trying to create a weapon script that has a running animation (and I was also thinking of adding some idle animations, but I'm going to get this working first then add those later). I only want this animation to play ONLY when you have the weapon equipped, I don't want to make the animation play when the players join the game. I have a basic script already made, but it says "character is not a valid member of model" The reason I want to make this animation on JUST this weapon, is because i don't want these animations to be on every character that joins the game. I know how to add weight values and I know how to import the animations, I just don't know how to actually make the animations work while the character is holding the weapon.

All of this was put into a local script into my actual tool

----------------------------------------------------------------------
------------------------------All the locals------------------------
----------------------------------------------------------------------
local tool = script.Parent
local canplay = true
local character = game:GetService('Players').LocalPlayer
local player = character.Character or character.CharacterAdded:wait()
----------------------------------------------------------------------
---------------Importing animaton/creating the int value---
----------------------------------------------------------------------
local int = Instance.new("IntValue")
    int.Name = "Seven"
local animation = Instance.new("Animation")
animation.AnimationId = "http://www.roblox.com/Asset?ID=619848002"
----------------------------------------------------------------------
tool.equipped:connect(function()
    int.Value = 1
    print(int.Value)
end)
tool.unequipped:connect(function()
    int.Value = 0
    print(int.Value)
end)
tool.equipped:connect(function(mouse)
    mouse.Button1Down:connect(function()
        print("Lol hi")
    end)
end)
----------------------------------------------------------------------
-------------------------Actual (Broken) animation code-----
----------------------------------------------------------------------
repeat
    wait()
until
int.Value == 1
if
    int.Value == 1 then
    while not player.Character do wait() end
    local character = player.Character
    local animateScript = character.Animate
    animateScript.walk.animation.AnimationId = "http://www.roblox.com/Asset?ID=619848002"
end

I basically made it so that the script creates a new int value then checks if that int value is 1 and if it is it should replace the character's walking animation. I might have another follow up question on how to add idle animations, but i have to get done with this one first lol.