Pani already shared all steps.
You need add required fields to your extract structure thru appending at SE11.
Go to SE11, enter your extract structure name, on next screen, click on append structure, enter your fields which need add. if your new to this, take abaper help.
once you added fields to your extrcat structure, you can unhide that field at RSA6.
later you need to write to logic to fill that enhanced fields. you can write code directly at include program ZXRSAU01 at SE38.
above steps all need to do at ecc system.
once you done above steps, do extraction at RSA3. if you see the data for added field then replicate data source into bw and activate it.
add related info object to your connected targets, do the mappings and activate transformations.
Thanks