You can use a code sample like this

--example syntax
CREATE FUNCTION us_filter(region STRING)
RETURN IF(IS_ACCOUNT_GROUP_MEMBER('admin'), true, region='US');

-- specific to your example
CREATE FUNCTION region_filter(region STRING)
RETURN
  CASE
    -- Users in USA-only group see only USA rows
    WHEN IS_ACCOUNT_GROUP_MEMBER('usa_users') THEN region = 'usa'
    -- Users in India-only group see only India rows
    WHEN IS_ACCOUNT_GROUP_MEMBER('india_users') THEN region = 'india'
    -- Everyone else sees nothing
    ELSE false
  END;

Then apply this function as a row filter on your table

ALTER TABLE sample_regions_table SET ROW FILTER region_filter_2 ON (region); --assuming your region column is called 'region'

Once the viewers query the dashboard, the filter will be applied.

You need to apply the function to the source table for row-level security to work. Is there a reason why you don't want to do this?