@ChristieAnn  You response was completely useless to me and failed to address the question - telling me things I already knew about how to create a quote - which seemed to be straight from Quickbooks on-line help.  

Your response should have been :

The option to create a quote from an existing or previous invoice is currently unavailable

Quickbooks currently does not have the feature to create a quote from an existing invoice

NOT:

Welcome to the QuickBooks Community, michael-green. I'll be sharing how Quote and Invoice feature in QuickBooks Online works. I'll also ensure you can achieve your goal by performing the alternative steps below.

A Quote is an entry that helps you start discussing details with your customer for a proposal for work you plan to do. While, an invoice is a list of goods sent or services provided, with a statement that needs to get paid in the future. With this, the option to create a quote from a previous invoice is currently unavailable.

For now, you can manually create a quote by copying the details from a previous invoice. This allows you to record a quote that matches the information from the existing invoice. Once done, you can open this article to see the detailed steps on how you can make attractive and professional-looking quotes in QuickBooks: Customise invoices, quotes, and sales receipts in QuickBooks Online.

After that, you have the option to link the existing invoice to a newly created quote in QuickBooks.

Here's how:

Click the Sales menu on the left panel and choose All sales section.
Find the invoice and open it to click the Edit button.
Click the arrow icon beside the Balance due and a quote entry appear.
Click Add and It looks like you’ve started working on this invoice. Should we add only the quote item lines, or create a new invoice for this quote? message shows, then select Create a new invoice to link the transactions.
Choose Save.
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Lastly, I'm adding this article to see details on how the Sales page gives you a great at-a-glance view of the status of your sales transactions, like open and paid invoices: View sales transactions in QuickBooks Online.

Please feel free to add a comment below if you have other concerns about managing your sales transactions in QBO. I'm always ready to help. Take care, and have a great day, michael-green.