How can i fix The humanoidrootpart?

Use waitforchild in case it hasnt loaded yet.

local commands = {}
local prefix = "/"
local function findPlayer(name)
    for i, player in pairs(game.Players:GetPlayers()) do
        if string.lower(player.Name) == name then
            return player
        end
    end
    return nil
end

commands.tp = function(sender, arguments)
    print("TP Function fired by" .. sender.Name)
    for i, playerName in pairs(arguments) do
        print(playerName)
    end
    local playerToTeleportName = arguments[1]
    local playerToTeleportToName = arguments[2]
    if playerToTeleportName and playerToTeleportName then
        local plrToTP = findPlayer(playerToTeleportName)
        local plrToTpTo = findPlayer(playerToTeleportName)
        if plrToTP and plrToTpTo then
            plrToTP.Character:WaitForChild("HumanoidRootPart").CFrame =  plrToTpTo.Character:WaitForChild("HumanoidRootPart").CFrame
            print("It fricking worked")
        end
    end
end
game.Players.PlayerAdded:Connect(
    function(player)
        player.Chatted:Connect(
            function(message, recipient)
                message = string.lower(message)
                local splitString = message:split(" ")
                local slashCommand = splitString[1]
                local cmd = slashCommand:split(prefix)
                local cmdName = cmd[2]
                if commands[cmdName] then
                    local arguments = {}
                    for i = 2, #splitString, 1 do
                        table.insert(arguments, splitString[i])
                    end
                    commands[cmdName](player, arguments)
                end
            end
        )
    end
)