Hello there, @sharon-johnston.
QuickBooks only allows you to change the start date of a recurring invoice template to future dates. If you enter past dates, the system won't allow you to save the template.
Let's go to the Recurring Transactions page to edit the template from there. Here's how:
Here's an article for your referece: How to Edit a Recurring Template.
In case you need tips and related articles in the future, visit our QuickBooks Community help website for reference: QBO Self-help.
That's it! Fill me in if you have other concerns about recurring invoice. I'll be sure to get back to you.