1. Go into your C: Drive, Users, Your Username, and then Saved Games. There should be a "Pokemon Reborn" folder and a file called Game.rxdata.
2. Rename the file something like Game1.rxdata. The game should no longer recognize it.
3. Start a new game and save. This will become your second save file.
4. When you want your old savefile back, change it from "Game1.rxdata" to "Game.rxdata". Then rename your second save file to something like "Game2.rxdata".
Hope this helps!