Okay correct me, if i was wrong understand your question …
Looks like you have an excel file’s name parent and child.
From parent row(0) you have unique values eg:1,2,3
From that parent file,you need to get that value (eg:1) for child file row(0) which contains some duplicate rows??
Like above you mentioned row(5) have false data!!
If this is your question,you need to find some other match’s from your parent and child file.
If your parent file “any column” contains like lk-20 has same has child file "any column"that contains lk-20…in this scenario you use if condition to write values for request_Id …