Search subitem and update

Hi there
I currently have 3 boards. One main and 2 “slave” boards for a warranty handling system.

The main board is an overview of machinery with serial numbers.

The slave boards are updating the main board with warranty requests and repairs.

1st slave board is creating a subitem (request) based on a serial number found as an item in the main board by search function in make. Subitem is created from make with serial number as main item and project number as identifier in subitem.

When a repair is done I need to identify the serial number which is found in a column in the main board (so far it is complete)
Trouble starts when I want to find the subitem with the request and update with repair.

When both files, request and repair exists in the same subitem the case is closed and main item is updated.

Any ideas?