data: row type i,
it_lt3 type standard table of lt3.
loop at it_lt3 into wa_lt3.
if wa_lt3-TPLNR = <captured value when you doubled clicked>
move sy-tabix to row.
endif.
endloop.
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-->declare an internal table it_lt3 of type lt3.
-->please write the code to capture the value of tplnr field when you double click [ you can use function module for this code].
-->the value that you will capture here put it in above loop [where i gave< >].
-->here row contain the actual row number where you doubled clicked.
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