Modefying the search pop-up inside the purchase invoice

I am new to frappe framework and ERPnext,
when I add multiple items under (New Purchase Invoice) as shown below:

it gives me the only two items I created so far in order to assign them to the supplier selected.
what I need to do as a task is adding two more rows in this pop-up ( price & quantity) for each item I have in the list.

Knowing that I am working 100% in the development mode and I tried to reach it within the code of the whole frappe-bench directory but I couldn’t spot it.

Can any one help me with this ?