Enter the editor of the map and go File -> Open Song folder
You will find the mp3 used in the folder that opens:
Open the timing setup panel using F6 and go into the "Timing Points" tab there. Mark all the timing points and press Ctrl+C to copy the timing points to your clipboard:
Now go to the editor song selection, drop the mp3 from the folder in there to create a new map.
After finishing the song setup, enter the timing setup panel using F6, click into the empty timing list and simply paste using Ctrl+V and confirm the dialog with "OK".