How do I clear all data from MarginNote 3

MarginNote 3 on Mac is ok, but I cannot make any new notebooks appear in iOS.
In fact, I deleted the iOS MarginNote app and redownloaded. Previous documents are there, but I have no notebooks. iOS stuck on “Fetching data from iCloud…”.

How do I clean MarginNote 3 from all data and restore from backup?
Where are the MarginNote Mindmap document/Notebooks located? I want to delete them too.
I want to be able to make a fresh install and restore from backup.

Thank you