Hello there, @tonya-villagiore.

Welcome to the Community. I can share some information about changing an invoice to an estimate.

While converting an estimate to an invoice is possible, changing it back isn't currently available. I encourage you to submit feedback to our Product Developers who determine features to be added in future updates based on requests from customers like you. 

Here's how:

1. Click the Gear icon and select Feedback.
2. Enter your suggestion and click Next.
3. Then, select Skip and send message.
4. Choose Category, then Send message.

You may also submit your suggestion via this link: QuickBooks Online Feature Requests. I’ll make sure to do the same thing on my end as well.

As a workaround, you can make a duplicate out of the first estimate. To do that, follow the steps below:

1. Select Sales from the left menu and choose All Sales.
2. Open the estimate you need to copy.
3. Click More and select Copy.
4. You may edit the estimate, then hit Save.

I've attached screenshots for your reference.

You may take a look at this helpful article for more details: How to duplicate an invoice or an estimate.

For estimate setup, function and common questions, you may refer to this article: https://quickbooks.intuit.com/community/Income-and-expenses/Estimates-Quotes-setup-and-function/m-p/....

Please let me know if you have questions or if you need anything else. I’ll be around to help. Wishing you the best!