How do I find a QBW file?

Welcome to the Community, @esukhdeo-704spor. You can find the .QBW file through QuickBooks Desktop. 

You may need to use a trial version of the QB Desktop and restore the backup to open it should you wish to export data to QB Online.

For more insights, here's a link with the details on how you can move your Desktop file to QB Online: Move your QuickBooks Desktop file to QuickBooks Online.

You also have the option to use a third-party app that can help you with integrating this directly into QuickBooks Online. You can visit this link: https://apps.intuit.com/app/apps/home.

I'll be around if you have any other concerns. Have a great day ahead.