local UIS = game:GetService('UserInputService')
local Player = game.Players.LocalPlayer
local Character = Player.Character

UIS.InputBegan:connect(function(input)
    if input.KeyCode == Enum.KeyCode.W or input.KeyCode == Enum.KeyCode.A then
        Character.Humanoid.WalkSpeed = 22  --run speed
        local Anim = Instance.new('Animation')
        Anim.AnimationId = 'rbxassetid://18686242456'
        PlayAnim = Character.Humanoid:LoadAnimation(Anim)
        PlayAnim:Play()
    end
end)
UIS.InputEnded:connect(function(input)
    if input.KeyCode == Enum.KeyCode.W or input.KeyCode == Enum.KeyCode.A  then
        Character.Humanoid.WalkSpeed = 16  --default walk speed
        PlayAnim:Stop()
    end
end)

I’m not sure how to fix this.