how to generate profit summary for last year for one particular produce/service

We're glad to have you here, Pmgcob. I'll help you see a profit summary for one particular product/service of last year.

In QuickBooks Desktop(QBDT), you can generate a Profitability by product report. This  would allow you to see what product is most profitable.

Here's how:

1. Run the Profitability by product report.
2. On the report window, select Customize Report.
3. Set the date range to the Last Fiscal Year. 
4. Click OK. 

Additionally, you can customize the report's filter to display All items and include all your inventories. 

I've also included this article to help you learn more about available reports in QBDT: Understand Reports.

Let me know in the comments if you need further assistance in generating financial reports in QBDT. We're always here to help you out.