Thank you for using Syncfusion products.
We have analyzed your requirement and you can edit the first cell when you have added a new row in grid by using BeginEdit() method in SelectionChanged event as shown in the below code snippet,
this.sfdatagrid.SelectionChanged += sfdatagrid_SelectionChanged;
void sfdatagrid_SelectionChanged(object sender, GridSelectionChangedEventArgs e)
We have created a sample to achieve your requirement and please find the sample from the below location,
Sample Link: SfDataGridFiltering.zip
Kindly let us know if this solution helps you.