how to fix?

you can do it yourself, you will need to remove bottom hose, empty old coolant into suitable container, re-fit hose, fill with correct amount of new coolant. when you first use the car, keep an eye on coolant level in res. tank, if you are losing coolant, you will need to check for any leaks. next time you use this forum, could you tell us the make/model/year of car, as this helps in giving advise a lot easier.

hope it helps
September 2010