Hi @Ammiraju Geddam ,
Welcome to our forum!
As i know, it's not available on Outlook Web App.
As a workaround, it's suggested that you could configure your account in Outlook desktop client and then try to export to a .csv file via File>Open & Export>Import/Export>Export to a file>Comma Separated Values>Choose the folder you want to export and click Next>Click Browse... to choose where to save>Next>Finish.
Hope the above help!
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