How to make a field from specific row of a child table read_only

Type Of Input’ is a select field. When ‘Type Of Input’ value is ‘System’ I want to make the ‘Value Field’ readonly and vice versa for ‘Manual Input’

May we know which field from which child table of which doctype ? Or am I misunderstanding the question?

In a child table if I want to make a field of a specific row readonly or not readonly. How do I do it.