Carpet stains

Have you got any bits of carpet left over from the fitting? If so could get a carpet fitter to cut and fit.

It's what I keep meaning to do for ours - not stains but chunks eaten by moths! - but haven't got around to it. Luckily not in too obvious areas.

Any of the carpet cleaners with Oxygen in them will shift stains but you do have to test first, I don;t think there is anything that will shift the yellow stain as humptydumpty as suggested get a rug

Sadly I suspect you didn't test on a small area out-of-sight first , must admit I wouldn't have either , salutary lesson here..