Hi Ha Jung,
Thanks for using Syncfusion product.
To move the selection programmatically, you could using the CurrentCell.MoveTo method. Please refer the following code example and the sample.
In this above attached sample, MonthShowFullWeek property has enabled. If you have disable this property, week days are covered by two rows. So, if you move to third row you could use the following code example.
To access the CurrentCell property, you could attach the Syncfusion.Grid.Windows.dll in your project.