You seem to be mixing two separate password managers
iPassword is a Third Party password manager
The new Password application was introduced in macOS 15 Sequoia
You may need to export from 1Password and import into DuckDuckGo
https://support.1password.com/export/
If the overall aim is to use the new Apple Password Application with DuckDuckGo Web Browser
I am not sure this can be gone
This does not mean it is impossible, I just do not know of it can be done
Some Third Party Browser, do have the ability to Import Passwords from the Default Builtin Browser >> Safari 18.0 in Sequoia
I do not know is DuckDuckGo is one of those that can