how do l top up the gear box oil on a t reg. ren laguna

On a manual gearbox there is an oil level plug on the front of the gearbox (looks like a plastic wingnut) Fill it up through this hole until the oil starts to run out, at that point the level is correct.
If it is automatic, u cannot top it up.
A dealer has to use diagnostic equipment to read the gearbox oil temperature to set the level.!!

Basiclly they put half a litre of oil in the gearbox, run the engine until gearbox oil temperature is 60 degrees & the drain excess oil out of the gearbox while the engine is still running