Hello decaf !

The code of the customized page is stored only in the database. If you want to edit the previous code you need to go to the Studio->Pages App. Then in the modules list find the one which you need (System or belonged to some app too) and there - the necessary page. It would be useful to review the following docs and videos:

https://github.com/unaio/una/wiki/Pages-Builder

https://www.youtube.com/watch?v=hhdog8nLjEk

and

https://www.youtube.com/watch?v=CuhZn3hfGbg