How do I refill my auto transmission fluid on my 08 hilux 4.0l petrol

Your owners manual will probably tell you what kind of transmission fluid it takes and it should show you were to fill it.

You refill transmission fluid through the tube where the dipstick is.. don't overfill it. Wait till the dipstick is low or dry while the engine is hot. Every year or two replace the transmission fluid to prevent leaks and overheating. A mechanic might need to reseal or replace the pan gasket.