New quotes modules How to update the current QLI based on field change?

Hi All,

We are moving old quote customisation to new quotes module in 7.9.4.

When quantity is changed, we need to update a custom filed for that specific QLI.

How/where to update the specific QLI only, based on the field change?

Any body has any idea how we can achieve that.

Regards,

Usman