you can use tJavaRow between your components. This component allows you to write java code and transform data. this component has input and output schema where you can specify input this component will take and output this component will give. section below for import will move to Advance Settings section of tJavaRow.
import java.io.*;
import org.apache.poi.ss.usermodel.*;
import org.apache.poi.hssf.usermodel.*;
import org.apache.poi.ss.util.CellRangeAddress;
You can write your java code in BAsic Settings section your refer to input data schema column by
input_row.column_name
and output as output_row.column_name
...(try to user GenerateCode option to see how input_row and output_row works)
Ideally for merging/transforming data you can also use tMap which can merge/transform rows and output the data to next level