How do I make a NPC chat?

The goal of this script is that when ever someone touch's the invisible block near the npc the npc will say G'day and then the players name who touched the block

button = game.Workspace.Talk

function onTouch(other)
	local human = other.Parent:FindFirstChild("Humanoid")
	if not human then return end
	local player = game.Players:GetPlayerFromCharacter(other.Parent)
	if not player then return end
	local color = "Blue" --This can also be "Green" or "Red"
	game:GetService("Chat"):Chat(script.Parent, "G'Day"..player.Name, color)
	wait(interval)
	end
button.Touched:connect(onTouch)

Use Dialog in Studio...