I can walk you through converting your online version to desktop, beetraveling.
I'd suggest logging in to your QuickBooks Online account using Internet Explorer since it's the supported browser of QuickBooks Desktop. We'll export the data from there. Then, we'll have to set up security settings in Internet Explorer to have a smooth export. Just a heads up, there are data that will and will not export due to feature differences. To know more about the limitations, you can click here.
Here are some links that will guide you through the detailed process of converting your data: Export and convert your QuickBooks Online data to QuickBooks Desktop.
After converting, you might want to cancel your QuickBooks Online subscription if you won't use it anymore since it won't automatically cancel though you transferred to a different platform.
Let me know if you have other questions. I'm just here to help you. Take care and wishing you all the best!