How do I make this server side instead of client side?

local gui = script.Parent
local players = game:GetService("Players")
local player = players.LocalPlayer
local run = game:GetService("RunService")
local sound = script.KillSound


gui.KillButton.MouseButton1Click:Connect(function()
local character = player.Character
if not character then return end
local head = character:FindFirstChild("Head")
if not head then return end
for _, v in pairs(workspace:GetChildren()) do
	if v:IsA("Model") and v:FindFirstChild("Humanoid") and v:FindFirstChild("Head") and v ~= character then
		
		if (character.Head.Position - v.Head.Position).Magnitude <= 20 and 		v.Humanoid.Health > 0 and script.Parent.KillButton.Timer.Visible == false then
			sound:Play()
			v.Humanoid.Health = 0
			character:MoveTo(v.HumanoidRootPart.Position)
			script.Parent.KillButton.Timer.Visible = true
			wait(1)
			script.Parent.KillButton.Timer.Text = "9"
			wait(1)
			script.Parent.KillButton.Timer.Text = "8"
			wait(1)
			script.Parent.KillButton.Timer.Text = "7"
			wait(1)
			script.Parent.KillButton.Timer.Text = "6"
			wait(1)
			script.Parent.KillButton.Timer.Text = "5"
			wait(1)
			script.Parent.KillButton.Timer.Text = "4"
			wait(1)
			script.Parent.KillButton.Timer.Text = "3"
			wait(1)
			script.Parent.KillButton.Timer.Text = "2"
			wait(1)
			script.Parent.KillButton.Timer.Text = "1"
			wait(1)
			script.Parent.KillButton.Timer.Visible = false
			break
		end
	end
end
end)

run.Heartbeat:Connect(function()
	local character = player.Character
	if not character then return end
	local head = character:FindFirstChild("Head")
	if not head then return end
	local cankill = false
	for _, v in pairs(workspace:GetChildren()) do
		if v:IsA("Model") and v:FindFirstChild("Humanoid") and 			v:FindFirstChild("Head") and 	v ~= character then
		
if (character.Head.Position - v.Head.Position).Magnitude <= 20 and v.Humanoid.Health > 0 and script.Parent.KillButton.Timer.Visible == false then cankill = true end
		end
	end
	if cankill then
		gui.KillButton.ImageTransparency = 0
	else
		gui.KillButton.ImageTransparency = 0.65
	end
	end)

Edit By JesseSong:

Please do not use deceitful means to get users to do your request. If you want to pay people to help you with your code you should make a portfolio in the Roblox Developer forums.

Make sure your question is paraphrased with a sentence explaining what is wrong and not working with the code. You can click on the hyperlink provided

Is this a GUI among us style kill button? Because you can't make GUI on server. You need to send a function from the client to the server then code the server. You will need a Remote event in Rep. Storage and code it so that when you press the GUI button it runs FireServer() I think that is what you were looking for? let me know if you have any questions

Here's what I would do

-- On the client

script.Parent.MouseButton1Click:Connect(function() --When you click the button
	game.ReplicatedStorage.Kill:FireServer()--Run the server
end)

--On the Server
game.ReplicatedStorage.Kill.OnServerEvent:Connect(function()
	--Put your code in here and have a good day :)
end)