Form update

Hello

i need to update a column (just a global var not in the DB) in my form (main item ) when i edit quantity in the same form (in other row, sub item in BOM of the main item).

first is it technically possible ?

if yes what function can be used to get these needed row to be updated (i had some check to get my row in question).

i hope that’s enough clear !

Thank you for suggestions