The dryer electric driagram identifies a RED L1 wire, a WHITE LN one, and other Black as L2. The suplpy cord has a RED, WHITE and BLACK wires and the green ground as well. How should I connect the wires to have the 240 V from the wall outlet and the 120V trough a 240 to 120 transfo?
Very often, these types of dryers are also marketed in Pacific Rim markets where only 240V is available. In this case, they build the dryer slightly differently, adding an internal 240V/120V transformer for the small number of 120V loads inside the machine (typically the motor).
I would start by getting the schematic for the 240V version of this dryer. Then compare it to the 120V schematic, and see what needs to change.
DO NOT - DO NOT - use a "step down" transformer without extreme care for how neutrals are bonded in the dryer and with your power supply. If a step-down transformer isn't applied painstakingly correctly, it would end up energizing the chassis of your dryer at 230V.
This likely won't work. Typically the motor and controls in a north American the dryer are designed for 120 volts. Only the heating element is a north American dryer is powered with the 240 volts. . North American power is delivered to your home in what is called split phase. There are two hots and a neutral. If you connect a load across the two hots, you get 240 volts. If you connect between one hot and the neutral you get 120. So in your dryers case, the heating element is connected across the two hot leads and the motor and controls are connected between one hot and the neutral. In the European system you have single phase. The hot is 240 and the other is the neutral. There's is no way to get the 120 off this system. To run the motor and controls.