How can I make a tool giver GUI like a trolling GUI?

You can do this with FindFirstChild(). Basically if we use FindFirstChild() then add the TextBox.Text into the "()" we are trying to Find the Child that has a name of the TextBox's Text.

First add a RemoteEvent into ReplicatedStorage, we will be firing this from the Local Script to then give the player the item.

Then add a Local Script to your Button.

Next add a Server Script into ServerScriptService.

Then add the following code: (You will probably need to change these locations inside the scripts to wherever your stuff is located.)

Local Script:

local Players = game.Players
local Player = game.Players.LocalPlayer
local Button = script.Parent
local RemoteEvent = game.ReplicatedStorage.RemoteEvent


Button.MouseButton1Click:Connect(function()

    local TextBox = Player.PlayerGui:WaitForChild("ScreenGui"):WaitForChild("TextBox")

    local FoundPlayer = Players:FindFirstChild(TextBox.Text)

    if FoundPlayer then
            RemoteEvent:FireServer(FoundPlayer, Button.Name)
    end
end)

Server Script:

local RemoteEvent = game.ReplicatedStorage.RemoteEvent

RemoteEvent.OnServerEvent:Connect(function(player, FoundPlayer, ButtonName)

    if ButtonName == "Name" then
        local Item = game.ReplicatedStorage.Item
        Item:Clone().Parent = FoundPlayer:FindFirstChild("Backpack")
    elseif ButtonName == "OtherName" then
        local Item = game.ReplicatedStorage.OtherItem
        Item:Clone().Parent = FoundPlayer:FindFirstChild("Backpack")


end)