Define switched?

Do you mean inverted?: Pressing the pedal reduces braking/acceleration, releasing the pedal applies pressure to the brakes/accelerator.
Do you mean swapped?: Pressing the brake presses the accelerator and vice-versa.

If you mean inverted:

Try clicking the invert button in LFS > Options > Controls > Axes/FF next to the brake and accelerator.



If you mean swapped:

You need to assign the brake and accelerator to the correct axis. You can do this in LFS > Options > Controls > Axes/FF. Click the accelerator button on the left, then press the accelerator pedal. Click the axis that moved. Do the same for the brake pedal.