If it's and older Diesel engine fill up the tank and run it when you have used a quarter of the tank fill it up again and then repeat this a good 4 - 5 times and you will dilute the contaminated fuel enough for it to not be a problem, if it's a new car under warranty what ever you do don't take it to the main dealer use a good independent garage it will cost you a fortune at the main dealer because they will replace everything from the tank through to the injectors and everything in line that has fuel in it.