Hi Nag
The easiest way to do it is to uploading data directly to demand management.
If you are planning to SOP, for example, you will end up transferring the forecast to demand management, so that they are relevant to MRP. So if you are not actually using SOP to create an integrated sales and production plan, then you can skip SOP and transfer those values directly to demand management.
If you choose this option, the easiest way to do it is creating a custom program to call BAPIs BAPI_REQUIREMENTS_CHANGE and BAPI_REQUIREMENTS_CREATE.
BR
Caetano