No kind of personal data is saved. The only data that is saved, is data about the fictional groups, accounts and transactions created in the app itself by the user. The user can not be identified by this data.
All the data is saved locally, which is why no one has access to the data but the user itself. The application only uses the internet connection to pull the latest currency conversion rates in order to convert between currencies.
In order to delete the data, which is locally saved, the user just has to delete the app and its data.