1. You have to decide which country/countries your customers belong.
2. Once decided, navigate to Customization > Forms > Address Forms.
* Image sample below: for Australia location only.
*If there is an existing setup for Australia only, you can edit it by clicking Edit.
*If none, you can click Customise from the Standard Address Form to create one.
3. Once you click Edit or Customize link, you can now customize the Address form.
4. Under Fields tab, you have to tick the box under MANDATORY section for each fields that you need to become mandatory.
5. Click Country tab, and select Australia (or based on your preference).
6. Click Save.
7. Navigate to Lists > Relationships > Customers and edit one of your customer record.
8. On Address tab, edit the address.
* Only selected countries from your address form are applicable for those mandatory fields you have selected. Make sure to select the correct Country for their address.