Once the Library is created, Memento allows you to adjust it anytime you need to. The principle is roughly the same as when you Create a Library from scratch. To start editing the library, tap on the Library you want to edit, then press the three dots menu icon in the top-right corner and choose Edit Library option.
Once opened, you can adjust the name, icon of the Library; add or remove Fields; adjust Relations for this library; set additional parameters such as Aggregation, Scripts, and Autofill.