Hi there, @melkhafif.
You can easily change the old transactions and add them to your Projects or Job. You'll want to open and edit the old invoices and expenses and change the Customer:Job name to the Job you preferred. Once done, the transactions will be added to the projects/job.
To easily track your sales and expenses using the job feature in your QuickBooks Desktop (QBDT) for Mac. You can check the Customer: Job status, date, and estimate totals section in this article: Customize customer, job, and sales reports in QuickBooks Desktop.
Additionally, I got you this article that gives the complete details in personalizing your invoice. This way, you can customize the invoice and make your business to stand out from the others: Use and customize form templates.
You're always welcome to comment here every time you have other questions in mind. I'm always here to answer them. Keep safe.