Hi Sven,
Thank you for your interest in Syncfusion products.
We suggest you to use "GridGroupingControl1.Table.Records[index].BeginEdit()" function to set edit mode for particular records.
For more details, please refer our Online Documentation:
http://help.syncfusion.com/ug_74/gridweb/defaultasp.htmlLet me know if you have any concerns.
Regards,
Bharath