The December 2020 version of the Raspberry Pi OS has yet again modified the way that application software selects the audio device. The OS now uses PulseAudio which is becoming the standard way to control audio on Linux operating systems. It has a number of advantages for Pi Presents:
- Audio outputs from more than one show can be mixed together
- Multiple USB audio devices can be used
- Bluetooth audio devices are easily supported.
I have updated both Pi Presents Beep and Pi Presents Gapless so that device selection from profiles works with both old and new versions of the OS.
There is a new configuration file /pipresents/pp_config/pp_audio.cfg. You can use this to change the audio system from pulseaudio if you are using an earlier operating system and, for Beep when using pulseaudio, configure USB and bluetooth audio devices. Instructions in ReleaseNotes.txt and pp_audio.cfg
There are a few bugs in the new operating system particularly if two monitors are used on a Pi4. Also I would recommend a new install rather than an upgrade as this seems to work better.
Stay safe.
Pi Presents 
Pi Presents is not installed in RPi OS out of the box. You need to download it as instructed in the Downloads page of this blog.
When installed there will be a file /home/pi/pipresents/pp_config/pp_audio.cfg. Also release notes and a manual in the /pipresents directory
This doesn’t help. There is no pipresents folder or pp_audio.conf. Where are these files? Where are the instructions?