If it's still fresh, scrubbing it under cold running water is the right way; carbonated water is even better, so if you've got some in your fridge you're in luck. If it dried up, you will need to be patient and work on it with a lot of lightly soapy water (ideally Marseille or Aleppo soap) and some kind of bleach; washing soda or a 5% solution of oxalyc acid or hydrogen peroxide are good choices, although the latter are more likely to fade the colour.

Exception: if it's a 100% synthetic carpet you're in luck, since warm water will work perfectly (but make sure it's your case, otherwise with organic materials warm water will make the blood clot).