The credits is located inside the project. (Go to the code of the sprite named "credits.sprite3" and you'll find a comment there.) Press T to restore the new background. Press R to restore the old background.
It's the first line in instructions. (this is pretty long) I remade for sprites, sounds, animations, or all, -10,000(all), -1,000(sprites and sounds), -100(sprites and sounds), -10(sprites and sounds), -0.1(sprites and sounds), 10^-8(all), 10^-7(all), 10^-6(all), 10^-5(all), 10^-4(sounds), 10^-3(sounds), 0.01(sprites and sounds), 0.1(all), 0.[unknown value](Half)(sprites), A(Dess)(sprites) E(14)(sounds), G(16)(Sounds), u(Unbe)(all), 0***(Exab)(all), Kent(all), _K(Kilo)(all), 10(sounds and sprites), 11(sprites), 12(sprites), 1A(sprites), 25(sprites), 50(sprites and sounds), 100(sprites and sounds), 1,000(all), 10,000(all), 100,000(all), 1,000,000(sprites and sounds), 10,000,000(sprites and sounds), ∞(Infinity)(sprites and sounds), Ω(Absolute Infinity)(sprites and sounds), ☉(Termina)(sprites and sounds), ⍰(Never)(sprites), Schwa Null(sprites), The End Forever(sprites), Fake Infinity(sprites), +1(sprites), Sunya(sprites), and Windowsfinity(sprites). I added i(imaginary), Desinkin, Epsilfiniti, 10*half, 100*half, 10+Half, 20, 110, 200, _A(Desskilo), _Kent(Kentkilo), __K(Milli), 100,000,000, 1,000,000,000, and 10,000,000,000.