Mail Merge: feature not found

We are trying to use LibreOffice Writer to make serial documents from Excel “Database” (.xlsx) that contains 8-9000 records.
We need to select a specific range of records (for example: from record 1000 to 1085) because we don’t need all of them everytime.
We can see in this doc. link (Mail_merge) that we can choose those records, but the problem is: where we can choose them??

Lubuntu 14.04 64bit, LibreOffice, Italian

I’m note sure il this will solve your problem as I only tried with a sample file of 21 rows.

As you can see in the image after clicking on “Save merged documents” a pop-up with options came up and I selected the range of files I wanted to save.

Hope this helps