How can manufacturers manage customers demand ?

By maintaing proper relationship with the customer ans their by understanding their need and market demand.

Also you can take a look on pervious year records for planning purpose.

Demand Management is not merely forecasting. Demand management strives to manage all the activities associated with discovering markets, planning products or services for those markets and then fulfilling the customers ‘demand’. 

Hi Anas,

As you mentioned managing demand contain demand planning,exploring new markets. need to alaboratemore about the marketing discovery elements & marketing mix