How Can I add filter by country and filter by segment in this:
Accounts are dependent dropdown set up on country.
You have to update the return type in the list and then you can use the parent list as dependent drop down0
Your assign action definition is missing 'filter by' conditions. You can add Country and Segment as filters in this action definition, only when they are available as properties in the (source) list from which you want to assign items ('A1 Accounts' here).
Assign action: https://help.anaplan.com/47f05095-13d0-4ed0-8caa-18cd4f301236-Set-up-an-assign-or-assign-only-action0