How do I make the text in a textbox change the text of something else?

Okay. First, insert a RemoteEvent into ReplicatedStorage and name it ChangeText. Next, insert a ServerScript into ServerScriptService. Leave it blank for now. Now edit the LocalScript and change it to this:

local ReplicatedStorage = game:GetService("ReplicatedStorage")

script.Parent.Parent.Parent.InfoGUI.InfoBoard.Aircraft.Aircrafttype.Text = script.Parent.Text
ReplicatedStorage:WaitForChild("ChangeText"):FireServer(script.Parent.Text, script.Parent.Parent.Parent.InfoGUI.InfoBoard.Aircraft.Aircrafttype)

This fires the RemoteEvent in ReplicatedStorage.

Now set the text of the ServerScript to this:

local ReplicatedStorage = game:GetService("ReplicatedStorage")

ReplicatedStorage:WaitForChild("ChangeText").OnServerEvent:Connect(function(player, text, textToSet)
    textToSet.Text = text
end)

This will set the text to the text of script.Parent.

Note: The LocalSscript will instantly run and fire the RemoteEvent. If you don't want this to happen, try putting the LocalScript code inside an event. For example, ClickDetetcor.MouseClick:Connect(function().