Download a free audio editing software application, such as NCH WavePad Sound Editor. Scroll to the bottom of the download screen once it opens in a new browser window and select the link that is compatible to the operating system you are using.
Click on the "Save" action when the download window opens to save the program to your computer's hard drive. Choose all of the recommended setting to install and run the program.
Click "File" at the top of WavePad when it opens and select the "Open File" tab to attach the MP3 file of your choice.
Edit the file for backward playback. When the song has loaded into WavePad, you will see its digital waves displayed in the editing platform. Click on the "Effects" tab at the top of the program and select the "Reverse" action.
Click on the "File" tab at the top of the program and select "Save File As." Name the file by typing a new name in the data form that will be provided. Click on the drop down menu next to "Save as Type" and select "MPEG Layer-3 (.mp3)" to convert the file to MP3 format automatically.