it is an automatic gear box
You can top up the box through the dipstick tube if required and make sure you use the correct oil for your car as the fluids are not all the same. Some manufacturers recommended a change of the type of fluid - Speak to the local dealer and parts dept - they will advise you on the updated fluid to use..
If that’s all OK then check all the electrical connections of the gearbox, remove each connector in turn and spray with contact cleaner. Check that the wiring to the gearbox is in good condition with no chafing or frayed wire
Shoud have mentioned the gear box oil was changed when the gear box sump was replaced. have not had any warning lights appear that would normally come on when oil low or there is an issue with the gear box.