Unfortunately, the import feature from iCloud Keychain (from macOS devices) is unavailable at the moment since no compatible passwords' file can be exported from iCloud.
For now, you can manually organize and upload a .CSV file to import all of your passwords to your account at once using a desktop device.
Find out how to organize a .CSV file here.
If you have any issues or difficulties organizing the file and importing your data, please contact our Customer Support team.