EXIT_SAPMM07M_001 : customer exit

Dear all ,

I have a requirement to pick the MIGO line item and header  text .

Header test I have picked from the table : MKPF .It is fine .

SELECT SINGLE BKTXT INTO ITAB-BKTXT FROM MKPF WHERE MBLNR = IMBLNR .     " Material text  

To pick the line item text : I tried below :-

SELECT SINGLE SGTXT INTO ITAB-SGTXT FROM MSEG WHERE MBLNR = IMBLNR .   " MATERAIL ITEM TEXT 

But MSEG do not have the line item text .

From where I can pick the text for line item .

I have searched and found that a customer exit :  EXIT_SAPMM07M_001  .

How to use this FM : what to enter in the import and export parameters .Please suggest any ideas .

But I am confused how to use it or is there any other way to pick the text ..

In MIGO  : transfer posting in the Where tab : there is a text which user enters .

I want this text to be picked up in my report .