Thank You. I tried to follow your instruction. It didn't work out the first time. Then I tried to do it again. But after that, I got authorization error when accessing the shop as below:

Error message:

Error to render compiling AST
AccessError: You are not allowed to access 'Fiscal Position' (account.fiscal.position) records.

This operation is allowed for the following groups:
- Invoicing/Billing Administrator
- Purchase/User
- User types/Internal User
- User types/Portal

Contact your administrator to request access if necessary.
Template: website_sale.products_item
Path: /t/t[2]
Node: <t t-set="combination_info" t-value="product._get_combination_info(only_template=True, add_qty=add_qty or 1, pricelist=pricelist)"/>

The error occured while rendering the template website_sale.products_item and evaluating the following expression: <t t-set="combination_info" t-value="product._get_combination_info(only_template=True, add_qty=add_qty or 1, pricelist=pricelist)"/>

Did I do something wrong? Is there a way to rollback what I set for the default value?

Thanks,
Wilson

This error seems to have another origin!
In any case to remove a default setting: activate developer mode->go to settings->technical->user-defined Defaults-> select and delete "Country (res.partner)"

Yes, I removed the user defined default "Country", but still it got 403 error.
Thanks anyway.

With the developer mode activated: go to contacts-> set filter "archived"->select Public User->Edit->Select desired Country->developer tools->set defaults->country=selected contry->all users->save default
I followed instructions as the above. But still, I need to select the country (no default country) when I process "Checkout". Any things I was missed.

I saw Country(res.partner) has already been set in Technical -> User-defined-Defaults.