I am transferring to Quick Books mid year. How do I enter my previous sales in one lump sum?

Hello, seajda1.

I'll be happy to give steps on how you can record the sales in bulk. You can use the Create Batch Invoices by following these steps:

1. Go to Customers > Create Batch Invoices.
2. Search the customer in the field and click the Add button. Tips: Press Ctrl on our keyboard and select the customers. 
3. Hit Next then select the Date and Template.
4. Add the invoice details and enter a customer message if desired.
5. Click Next to review the invoices, then select Create Invoices. You can select Print or Email.
6. Click Close.

I've got this article for reference: Enter transactions by batch in QuickBooks Desktop

Please let me know if you need more help with the process. I'll be happy to lend a hand. Take care and stay safe.