Hi Mukesh,
The answer you are looking for is within this thread.
Though not sure if that applies to your version of SAP, it would normally use search string functionality (Bank accounting > Business transaction > Payment transaction > Electronic bank statement).
If MT940 always receive the 'HSBCN + 11 digits number, you can maintain HSBCN########### as a search string and assign to your house bank. Ensure that the target field is a note to payee (Payment note).
hope that this helps
Taro