How do I change the “Hey”greeting at the beginning of emails sent with invoices?

Hello, beverley_briggs-.

I'll share the steps where you can update the information.

You can modify the email subject or message by following these steps:

1. On the left panel, click Invoices.
2. From the Action column, click the drop-down arrow next to Send invoice or Mark as paid and select Edit. 
3. In the invoice page, click the drop-down arrow located in the lower right-hand corner and select Preview. 
4. Edit the Email Subject or Message. 
5. Click Send afterwards.

To view the other ways on how you can send the invoice to your customers, feel free to read this article: Create invoices in QuickBooks Self-Employed.

If you have any follow-up questions or need help with other task in QuickBooks Self-Employed, please let me know in your reply. I'll be around to help. Have a good day ahead.