Can I fit Anti freeze to a Citroen Echo myself and how do I do it

pour it in your radiator,,,,,,,,,,,undo cap ,,pour in

Put it in your radiator via the radiator cap.
Do not do it when the engine is still hot, you will scald yourself.
Check with your user manual as some engines have aluminium parts that can suffer corrosion over the years from some types of anti-freeze.

Also check the dilution, normally it is 30 to 50% anti-freeze and 70 to 50% water.

Better do this with a cold engine. Open the radiator cap, fill in the antifreeze-water solution. If you had a loss of cooling liquid before, you should also make sure no air is still present in the circuit. For this, you must check the level after filling the liquid and after around one week of normal engine use. Meanwhile, keep an eye on the temperature level and watch for any abnormal behavior of the temperature indicator.

Best to bolt it to the wishbone. Improved performance.