Make a copy of the clip and reload it into Movie Edit; then right click the audio track and you should see an option that says "Edit wave externally." This will bring you to Magix Music Editor."
When it opens the wave will be on the screen and you will see that there are various effects tools with filters for noise reduction, declipping, dehissing and so forth. Using the cursor you can isolate a certain part of the track if you want. (And I began by saying "make a copy" and "reload" the clip because: for one, once you're in Music Editor, unless you do a "save as" I'm pretty sure any changes you make will permanently affect the source file; and two, I've found that after working with a clip in Movie Edit it sometimes doesn't provide the "Edit wave externally" option.)

That said, and as frustrating as this sounds, it might be in your best interest to re-record the track because running the likes of noise reduction filters can really sabotage the overall quality and sound of the track and make it worse overall. It may sound like an oxymoron but the premise is like an Auto Body painter that brags about how good he is at fixing the runs in his paint job.
Moreover, I'm not sure what filters you can apply to eliminate the annoying echo you speak of. In any case, good luck.