Please note: This feature is only available starting with version 3.7.0 of the Gnosis Safe web interface.
The address book is stored in your local storage of device or browser. That means the information is not shared to any external service. It can be accessed via the side bar.
The export button can be found in the top right corner of your screen, next to the create entry button.
This will give you a csv file with all your address book entries.
The import button can be found in the top right corner of your screen, next to the create entry button.
After selecting a file and clicking the import button, your existing address book will be updated.
Existing entries with the same address will be updated with the names from the file.
Existing entries with an address that does not occur in the file will not be touched.