DO $$
DECLARE
  column_record record;
BEGIN
  FOR column_record IN
    SELECT table_schema, table_name, column_name
    FROM information_schema.columns
    WHERE table_schema = 'public'
      AND data_type = 'timestamp without time zone'
  LOOP
    EXECUTE format(
      'ALTER TABLE %I.%I ALTER COLUMN %I TYPE timestamptz USING %I AT TIME ZONE ''UTC''',
      column_record.table_schema,
      column_record.table_name,
      column_record.column_name,
      column_record.column_name
    );
  END LOOP;
END $$;