Unfortunately that is not possible once a video has been made Anaglyph - there are no seperate Left / Right video streams.
You need the original video streams (files) from the camera and import them into MEP.
If this camera works as others I have seen then you should find you have 2 video tracks - one left stream and the other the right stream - and one audio track.
You can mute the left or right video stream (channel) but not the audio and use this to create the 2D video.