@Jsadhik - While I am intrigued by the use case on why you would like to download the data of the dataset rather than visualizing it, I believe you can’t do it directly from Dataset. However, you can bring all the data into a Table visual and try the export option to get the unaggregated data exported into an Excel or CSV. Please see the below link:
However, it would be good to know your use case on what you are trying to solve by downloading the entire dataset data in Excel. Perhaps there are better ways to do it beyond QuickSight if you don’t have a requirement to visualize the data. Hope this helps!