Keeping the video and audio linked

[Sheff_Joy]

Basic rookie question - I have imported a video file made on a phone into DVR and it has separated the vid and audio. When i then import another phone video and try to move the first video to synch with the second, its vid and audio are unlinked! How do I keep the link between the video and audio for each clip? - I have found advice on auto synching a separate audio clip but my originals are recorded into the same mp4 yet DVR separates them and unlinks them! Please can someone help