Double-click the desktop icon to launch the digital audio workstation with which the song was recorded. Depending on your digital audio workstation preferences, either the last saved session or a blank session will open.
Open the relevant session if necessary. Click "File" and select "Open" or "Open Recent," depending on which digital audio workstation you are using.
Click on the first drum channel in the channel strip to highlight it. This assigns subsequent actions to this particular audio file, rather than the mix as a whole. If you haven't named your tracks, hit "Play" and click "S" on each channel in turn. This mutes everything but the selected channel, enabling you to hear the track in isolation to determine what it is.
Click "Send To" and select "Bus 1." In audio, a bus is a mix channel for routing. By routing multiple tracks to a single bus, you can control all of the routed audio using a single set of parameter controls. Routing tracks to a bus effectively renders them as one track.
Click on the next drum track and route it to the same bus channel. Repeat this process for each drum track. Once all drums are routed to the same bus, you can export that track as a single file. The resultant audio file is called a submix.
Export the bus channel audio. The method for doing this varies slightly depending on which digital audio workstation you use, but you do it from the "File" menu. For example, in Logic, click "File," "Export As" and select your preferred file type, such as "MP3" or "Wav."
Name the drum submix file when prompted.