Step 1: Remove the ESC enclosure.
Step 2: Disconnect all the cables.
Step 3: Swap the connection of the two motors.
Step 4: Turn on the board and scroll the wheel of the remote. Here are 2 results: ❶ If the same motor does not work, that means the motor is broken. ❷ Instead, if the original non-rotating motor can rotate, that means the ESC is broken.