Hi Nikitha,
Greetings from Syncfusion support.
The reordering on grouped columns is a new functionality implemented to be released in our 2020 Volume 1 Release. We had mistakenly refreshed the online documentation site before the main release. We regret the inconvenience caused. This feature will be available from our upcoming 2020 Volume 1 Main release which will be rolled out by the end of March 2020.
We appreciate your patience until then.
Let us know if you have any concerns.
Regards,
Sujith R