If you're reheating it from the fridge, place it in the microwave for a few minutes. If you want to heat it on the hob, place it in a saucepan and simmer on medium to low heat for 15 minutes, stirring frequently. If you're reheating it from frozen, take it out of the freezer and leave to defrost for a few hours. Then, simply follow the instructions above to heat it up.