The camera change activates when the player clicks a GUI button.
Script:
local Camera = game.Workspace.CurrentCamera
local Players = game.Players.LocalPlayer
local button = game.StarterGui.Camera.TextButton
button.MouseButton1Click:Connect(function(player)
repeat wait() until Players.Character
Camera.CameraType = "Scriptable"
Camera.CFrame = workspace.Rocket.Rocket.CamPart.CFrame
end)

1 comment
You can't reference items in game.StarterGui, these are prototype instances that are copied into the local player's PlayerGui (child of the Player)