airport screen for my roblox game?

hello all im trying to make an airport game but i cant get my code to work what im trying to do is when the player sits in the check in seat a GUI pops up where they can type gate number departing time etc and when they press submit it puts the text on the screen behind them here my code for one of the boxes

script.Parent.MouseButton1Down:connect(function()

local screenbrick = script.Parent.Parent.Parent.Value.Value.Screen

    local TextBoxObject = whatever

    TextBoxObject.Text = ("test") --> simple    

    screenbrick.SurfaceGui.Frame.DepartureTime.Text = script.Parent.Parent.DepartureBox.Text

end)

but when i run the code it just says enter text here on the screen behind me