How to I make a database for linkedleaderboard kills only?

Try the following in a regular script:

Oh yeah, by the way, make sure the leaderstat you want to save is called "linkedleaderboard kills", because that's what I placed in the script. if it's not, please change the leaderstats name. You also need to delete your script to create the leaderstats, and the one that you're trying to use, to save the leaderstats: This script makes both! :D

function DataHandler(p,o,key)	-- DataHandler(Player, Object [, Key])
	local types = {
		IntValue = "Number";
		NumberValue = "Number";
		ObjectValue = "Instance";
		BoolValue = "Boolean";
		StringValue= "String";
	}
	local t = types[o.ClassName]
	if (not t) then return end
	key = (type(key) == "string" and key or o.Name)	-- If it's a string, keep it the same, ELSE change it to the object's name. Allows 'key' to be an optional argument.
	key = (#key > 0 and key or key.Name == o.Name and o.ClassName or o.Name)	-- If length of string is greater than 0, keep it the same
	if (not p.DataReady) then														-- ELSE if it is equal to the object's name then that means that the
		p:WaitForDataReady()														-- object's name is blank, therefore make 'key' the ClassName.
	end																			-- ELSE make it the name of the object.
	local Save,Load = p[("Save%s"):format(t)],p[("Load%s"):format(t)]	-- Steal the load and save functions from the player
	o.Value = Load(p,key)	-- The same as p:LoadTYPE(key). Since it's no longer a method, the player must be the first argument
	local lastV = o.Value
	o.Changed:connect(function(v)
		lastV = v
		delay(1,function()						-- Give a 1 second buffer to see if the value changes anymore. If so, stop the operation. If it goes 1 second without changing, it will automatically save.
			if (lastV ~= v) then return end	-- This way you don't save a value 20 times in 1 second if it changes constantly. Lower data processing = less lag
			Save(p,key,v)
		end)
	end)
end


--A table for holding all the player's leaderstat values
local playerLeaderstats = {} 
 
game.Players.PlayerAdded:connect(function(player)
	playerLeaderstats[player] = {}
	playerLeaderstats[player]["Kills"] = 0
	local leaderstats = Instance.new("Model")
	leaderstats.Name = "leaderstats"
	leaderstats.Parent = player
	local kills= Instance.new("IntValue")
	kills.Name = "Kills"
	kills.Value = playerLeaderstats[player]["Kills"]
	kills.Parent = leaderstats
	
	DataHandler(player,kills,"Kills")
end)