Fix invoice item list

I am not good with QB. I just added an item called Poduct Sample to my invoices item list (Manufacturing and Wholesale Edition). I mistakenly the item to service instead of inventory part. I went to edit that, but the line where service (the top of the window) is grayed out. So, I tried to delete it to start over but it says I am using Product Sample on an invoice somewhere. It's possible. My next idea was to find the invoice(s) and alter the item on them to "free" it so I could fix or delete the item. But how can I search the invoices to find that/those? Using Find in invoices only lets me search by Job Name and I have a couple of thousand invoices. So how can I try to locate the invoices I want to see? The other question, will I be able to change the item from service to inventory part if I can alter the old invoice(s)