Hi Kumkum,
To do an automatic clearing as you have mentioned, you will have to enter the Customer number in the Vendor master (Control tab) and set 'Clrg with Cust' in Payment transactions accounting view.
Also, similarly in the customer master, you will have to enter the 'Vendor' in General data control view as well as 'Clearing with Vendor' in Company code data payment transactions.
Then, during automatic payment transactions F110 clearing is made with the corresponding vendor account, and that during manual clearing procedures, the items of that vendor account are also selected.