How do you convert an already existing estimate to a new project once the estimate is approved by client?

Hi there, christopher.lewi.

I suggest going to the Sales tab. From there, you can look click the estimate you created and change the customer's name to a new project's name. This way, you'll be able to convert an already existing estimate to a new project after the estimate is approved by the client.

here's how:

1. Click on the Sales tab at the left pane.
2. Refer to the Customers sub-tab.
3. Select the customer’s name.
4. Locate and open the estimate. 
5. Tick on the drop-down arrow in the customer field.
6. Look for the name of the new project and select it. You may also apply any changes to the transaction if necessary. 
7. Press on Save.

In case you'll be using progress invoices on your future transactions, I've got here some references that you can check out on how you can add a project estimate summaries and on how the project works:

• Learn how to include estimate summaries on your progress invoices in QuickBooks Online.
• Projects FAQ

I'm just a few clicks away if there's anything else that I can assist you with. I'll make sure you're all set. Have a great day!