Hi Monikandan,
Now since you need to add the fields from your target structure you should use XSLT mapping over your message mapping to for the two fields SHIPDT_GROSS_QTY and SHIPDT_SHIP_QTY to get the summed amount.
Like for example the logic being:
<xsl:value-ofselect="sum(row/access/SHIPDT_GROSS_QTY)"/>
Similarly for second one.
Just complete the code with proper tagging it would work.
Regadrs,
Sachi