Install Jython

Burp relies on Jython to provide its Python support. You will need to download (https://www.jython.org/download) the "Standalone Jar" version and configure Burp with its location (at Extender / Options / Python environment).

Install extension. Burp > Extender > Burp Extensions > Add; Extension Details > Extension type: Python; Extension file: path/to/report2text.py