The dipstick on the auto transmissions is located on top of the transmission unit between the battery and engine.
To check the level, start the engine and allow to idle for a couple of minutes with the selector in the 'P' position. Withdraw the dipstick from the tube and clean it . Reinsert dipstick into tube as far as it will go and ensure the level is between the MAX and MIN markings.
If topping up is required, add transmission fluid via the dipstick tube - you will need to use a funnel to avoid spillage.
You may find that the transmission fluid requires renewing. The drain plug is located on the RHS of the gearbox just below the driveshaft. 🙂