How to add .sws notebook files to SageNB so that I can convert them into .ipynb?

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I have a bunch of .sws files, that were made (I suppose) with the now-deprecated sage notebook. Currently the default notebook application for Sage files is Jupyter, which cannot open these files. I tried

1. Using the built in "sagenb-export" command (ask.sagemath.org/question/35873/how-to-automatically-convert-many-sws-to-ipynb/) and also a standalone package (github.com/vbraun/ExportSageNB) in order to do it, but the notebook list in sagenb is empty (sagenb-export --list shows an empty list) and I could not make it to convert files that are not on this list. When running sage -n, there is an option "Convert old notebooks to Jupyter", but the list below that line is empty as well Is there a way of importing .sws files into this list?

2. An alternative way was to use the -sws2rst and -rst2ipynb flags that I found in an answer here (ask.sagemath.org/question/35873/how-to-automatically-convert-many-sws-to-ipynb/?answer=38197#post-id-38197), but that gives me ModuleNotFoundError: No module named 'sagenb'. Is it possible to install the sagenb module?