Start the mower and allow it to run. Do not engage the blade and make sure the brake is engaged.
Lift the engine cover and then remove the transmission fluid dipstick. Wipe it clean with a rag, place it back into the dipstick tube and then pull it out again.
Examine the reading on the stick. If it falls below the low level indicator, add transmission fluid. If it is not low, replace the dipstick and close the engine compartment.