Hi there, @kellygirl!
Currently, there isn't an option to customize or import an invoice template.
In addition, you can only import banking transactions with your QuickBooks Self-Employed.
Nevertheless, here's how you can create an invoice:
Once done, you can now successfully create an invoice. In addition, I've included a detailed in creating an invoice.
Fill me in if you have any other questions about invoices. It'll be always my pleasure to lend you a helping hand.