This stuff is the key its called PolyWatch see https://www.watchobsession.co.uk/products/polywatch-acrylic-glass-scratch-remover we keep it all the time and it works really well. Toothpaste is potentially a quick fix if the scratches not too bad but I would look at using PolyWatch if there's no actual physical damage to the crystal alternatively we can probably replace it but nine times out of ten Poly does the trick.
Richard Smith
I have a Rolex Submariner from 1987 but the Plexiglas crystal is badly scratched can you replace it?