Structured does not require its users to set up an account. Instead, all of your data is stored in your iCloud. If you want to remove the app data of Structured from your iCloud, you can do so in your device's settings by following the instructions on the Apple support page: Manage your iCloud storage.
On our servers, we only store anonymous analytics data to help improve the app. If you do not want us to store this type of data, you can opt out of this option and delete the analytics data we have already collected from your app. Simply open the Structured ⚙️ settings and select the Analytics section. Here, you can deselect the option Share Anonymous Analytics and delete already stored data by tapping Request Data Deletion.