You cannot re-import an MZT file into Mezzmo since MZT is not a valid media file format extension - it is an internal file extension only used by Mezzmo's transcoder engine. If you know what the file format should be, then you can copy the MZT to another folder location and replace the MZT file extension with what it should be (such as MKV, AVI, etc.). Once done, you can add this into Mezzmo.