How can I turn on/off the pattern day trade protection?

By clicking "Setting" → "Trade Preference" → "Order Placing Settings", you can find the switch of "Pattern Day Trade Protection", and decide whether to turn on the protection.

If you turn on the "Pattern Day Trade Protection", we will notify you when you are making the second and the third day trade in five trading days, and we will prevent you from placing the orders which might mark you as a PDT(the protection cannot guarantee that you won’t be marked as a PDT).