I have created wpf mvvm App from below link now I want use existing te

I have created wpf mvvm App from below link now I want use existing texboxes to add new data to datagrid, currently in app binding data to datagrid on form load and on datagrid row selection data binds to text boxes to update as expected from link I have added one button AddData I am not getting how add new data https://stackoverflow.com/questions/30643782/how-to-bind-a-datagrid-row-with-text-boxes-in-wpf-mvvm