How Can I Add A Respawn Keyboard Shortcut?

You'd need to use UserInputService. First, insert a LocalScript into StarterPlayer > StarterCharacterScripts. Next, insert a RemoteEvent into ReplicatedStorage and rename it to "ResetCharacterEvent". Write the following code.

game:GetService("UserInputService").InputBegan:Connect(function(input, gameProcessedEvent)
    if input.KeyCode == Enum.KeyCode.R and not gameProcessedEvent then
        game:GetService("ReplicatedStorage").ResetCharacterEvent:FireServer()
    end
end)

The InputBegan event fires when an input is pressed (Keyboard, mouse, etc.) Then there's and if statement checking if the input the player pressed is R on the keyboard and if the player isn't in chat. This would be very important, because you wouldn't want a player typing "R" in chat and getting reset.

Now, insert a regular script into ServerScriptService and write the following code in it.

game:GetService("ReplicatedStorage").ResetCharacterEvent.OnServerEvent:Connect(function(player)
    player.Character:BreakJoints()
end)

It will check if the reset event is fired (when the player presses "R") and then it will kill the player by breaking its joints.

--Make It A LocalScript

local Player = game.Players.LocalPlayer.Character
local UIS = game:GetService("UserInputService")
UIS.InputBegan:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.R then
        Player.Humanoid.Health = 0
    end
end)

And if you want them to have a delay between them (This is delay of 15 seconds change the wait(HOW MANY SECONDS YOU WANT) put a IntValue in the localscript and put the value to 0 and name it Val

local val = script.Val.Value
local Player = game.Players.LocalPlayer.Character
local UIS = game:GetService("UserInputService")
UIS.InputBegan:Connect(function(Input)
    if Input.KeyCode == Enum.KeyCode.R and val == 0 then
        Player.Humanoid.Health = 0
    val = 1
    wait(15)
    val = 0
    end
end)

Also to make them HOLD R for a few secs to reset then do

--Also a LocalScript
local Health = game.Players.LocalPlayer.Humanoid.Health
game:GetService("UserInputService").InputBegan:Connect(function(inpObj, GP)
    if inpObj.KeyCode == Enum.KeyCode.R then
        i = i + 1
        local tmpVal = I
        wait(3)
        Health =  0
        local held = true
        local con
        con = inpObj.Changed:Connect(function(prop)
            if prop == "UserInputState" then
                con:Disconnect()
                held = false
                return

This isn't a request site but ill make one. Try this you will have the make the players variable first Put in serverscript service or if that dosen't work put it in workspace, local script.

local Player = game.Players.LocalPlayer
function Keybinds(KeyCode)
    if KeyCode.KeyCode == Enum.KeyCode.R then
        player.Humanoid.Health == 0 
end

Hello, this would be how you do it:

--local script:
local debounce = false --The player can only reset once per 6 seconds
game:GetService("UserInputService").InputBegan:Connect(function(key)
    if key.KeyCode == Enum.KeyCode.R  and debounce == false then
        debounce = true
        game.ReplicatedStorage.reset:FireServer() --add a remote event in the replicated storage, and call it reset
        wait(6)
        debounce = false
    end
end)

Add a remote event in the replicated storage called "reset".

--Server Script
game.ReplicatedStorage.reset.OnServerEvent:Connect(function(plr)
    plr.Character:BreakJoints()--break joints kills the player
end)

Hope that helps!