Dear Nikitha
For this you need to set up the entire EWHT configuration in SAP. Please refer to below link for details of configuration;
Step by Step document for Withholding Tax configuration
Before going ahead with the configuration, you need to gather the business requirement.i.e whether they want to get the WHT deducted at the time of Invoice or at the time of Payment, %age of WHT to be deducted etc etc.
Hope it is clear now.
Regards
Syed Zia Abbas