How to Use SELECT DISTINCT
MS-Access lacks window functions, so you'll need a subquery solution. I think this would work:

SELECT c.* 
FROM Customers AS c
  INNER JOIN
    ( SELECT CustCity, MIN(CustID) AS CustID
      FROM Customers
      GROUP BY CustCity
    ) AS m
  ON (  m.CustCity = c.CustCity
    AND m.CustID = c.CustID
     ) ;