Your client will need to export their data into a CSV file, then they can import it to QBO. You can share this article with them: Move your Quicken data to QuickBooks Online.
If there's anything that I can help you with, feel free to reach back out.
Have a good one!
I would suggest contacting Quicken's Support to know your options. You can also look for an app that can transfer your data to QBO.
Alternatively, you can connect your bank accounts to QBO. That way, you can download your transactions and add them to QuickBooks.
If you have other questions in mind, you can always go back to this thread.
There is no direct way to import data from Quicken to QuickBooks online.
You have to export various reports in CSV, massage them as per QuickBooks online import template, and import in QuickBooks Online.
Please check this link:
Where we are an exclusive migration partner with Intuit for Australia
You can also have a look at the FAQ section for the migration from Quicken to QuickBooks Online.
If you’re interested, feel free to DM us.