Hi! Sorry, just seen the review -- have you been able to follow instructions here? https://github.com/karlicoss/promnesia#install
Feel free to reach me on the email, might be easier and quicker to communicate.

P.S (2020-11-26) I've just released a new update which allows the extension to work without the backend which should make it considerably simpler to try out (just need to install the extension). I've also added lots of updates to the documentation & setup process, so perhaps this would help! https://github.com/karlicoss/promnesia#try-it-out