It is not difficult, you did not mention which version of Music Maker do you use?
I got MMM 16 Premium
You got two options, before you proceed it is wise to save original first then use
copy in Music Editor.
1. When Music Maker is open
click on
Efffects/Audio/Edit audio in external editor (Ctrl+Shift+A)
Then click on Effects and you can choose example
Dehissing, try by some changes on knobs when you are satisfied you must export that as audio using File. or if you like you can just click ok normally in the Music Maker arranger the audio should be changed some times it also change the original therefore be aware.
2. If you know where you Music Editor is click on Icon
from File/Load audio file
now you can edit as you like then
File/Export audio (choose formats)
Music Eidtor is very good tool if you know how to use. Go and try. My advise always use copied audio not original.