I making a script for my game that resets the leaderboard status but its not working?

I rewrote this to give you a better idea of how it should look. You can add some more if checks but if the rest of your code is working correctly you shouldn't have any errors.

Your code has several issues, but most importantly this 'Amount = 0' doesn't do anything. You need to create the values on entry, not at some interval.

--a simple function to iterate all players turning the specified objects value to 0, this is more flexible since it allows for any amount, any stat(inside leaderstats), and any group of players
function resetStat(players,stat,amount)
    for i,v in pairs(players) do
        v.leaderstats[stat].Value = amount
    end
end

--this adds the leaderstats folder and corresponding values when player joins the game
game.Players.PlayerAdded:Connect(function(Player)
    local leaderstats = Instance.new("Folder")
    leaderstats.Name = "leaderstats"
    leaderstats.Parent = Player
    local Kills = Instance.new("IntValue")
    Kills.Name = "Kills"
    Kills.Parent = Player.leaderstats
    local Deaths = Instance.new("IntValue")
    Deaths.Name = "Deaths"
    Deaths.Parent = Player.leaderstats
end)

--much cleaner, right? 
while wait(300) do
    local players = game:GetService('Players'):GetChildren()
    resetStat(players, 'Kills', 0)
    resetStat(players, 'Deaths', 0)
end