To save a track with alterations, use the save button at the top of the editor, the box with the down arrow. The new track will have the current tempo and pitch settings applied and can be found in the My Creations section of the app.
Detailed Save to My Creations Step by Step
Tap the save button at the top of the editor window
Change or keep the track's filename and title. By default both are filled with the original track title appended with the pitch and tempo alteration values. The filename is used by the OS, and the title is what is most commonly displayed as the track title in music players.
A new track has now been created. You can choose to use it outside of Music Speed Changer at this point by sending it through your available apps or by saving it to files. If you want to continue in Music Speed Changer, you can just dismiss this step by tapping the x in the top right.
To access your new track, go to My Creations. My Creations is the last bottom tab of the app, and the place where you can find all tracks you save from the editor.
Tap here for more info on My Creations section