How to create a gantt chart within an existing table?

Hi @rahulkoc, We will include Gantt Chart type as a feature request however in the interim you will have to create calculated fields to achieve something similar. Please refer to below links.
Prior Community Response : Gantt Chart Visualization Type - #2 by Tatyana_Yakushev
Sample From Arena : Gantt Chart Visualization Type - #5 by Tatyana_Yakushev

Hope this helps. I am marking this reply as Solution, but let us know if you have any additional questions. Thanks for posting your questions on the QuickSight Community Q&A Forum!

Regards,
Karthik