You
could use the Timeline to do the job with similar steps
to the following.
1. Put one of the two clips on the video track since
both have the same video.
2. Mute the audio for the video clip by right mouse
clicking on the clip and selecting "Audio -> Mute"
from the clip menu.
3. Put the clip with the left channel audio on the
1st audio track.
4. Put the clip with the right channel audio on the
2nd audio track.
5. In the 1st audio clip, select "Audio ->
Duplicate Left" in its clip audio menu.
6. In the 2nd audio clip, select "Audio ->
Duplicate Right" in its clip audio menu.
7. Select "Output to Left Channel" in the 1st
audio track menu by right mouse clicking on the track
button on the left.
8. Select "Output to Right Channel" in the 2nd
audio track menu.
9. Save the timeline to a project file to protect
your work by selecting the "Save As" from the
upper left corner 4 button box of the timeline.
10. Press the Export button (the red one on the right
of the timeline).
11. Select the "Automatic" template and the
export job will start automatically without minimum
re-encoding of the video.
12. Check the output clip in the Input monitor by
finding it in the Clips page of the Project
Manager and double clicking on it.