Hi there, welcome to the LUG. Here is how I would do this:
Assuming your stereo audio file is already placed as an audio region in logic's main window, running through a stereo channel strip/track, click hold the channel mode icon to the left of the input button on the channel strip. This opens a dialogue, which will allow you to choose between mono, steroe, left, right and surround. Choose left. Now, copy the audio region in the main window onto another track, go to its corresponding channel strip, long click and choose right. You now have the left signal of the audio file playing through one mono channel, the right signal through another. You can now treat these two signals independently of each other.
If you actually want to create two mono files corresponding to the left and right parts of the stereo file, leave the stereo file as it is, but now, short click on the channel mode icon, this splits the stereo output channel into two mono output channels. each has itso own bounce button, which you can use to create a mono file.