SMW19 is used to Copy BDoc message into another. So fill the BDoc ID, SITE ID(if you know), Let the BDoc state be I01 and fill in the Flow Context. You may check other options like "read receivers" etc.
Click on "Read values in parameters" and press F8. This takes you inside the metadata of BDoc and then you can edit it accordingly.
Once you're done, you'd see a new BDoc created in SMW01 with the BDoc ID as something like <USERNAME>+GUID.