How to write to an empty column in Excel

I currently have an excel file with some of its columns empty. How can i write to the first empty column in the data table? In the screen shot i attached how can i write into C1 since it is the first column. I have used a for each activity to fetch each column.ColumnName but i get Column1, how can i write into Column1?

See this sample -

Main.xaml (9.4 KB)
EmptyColumn.xlsx (8.2 KB)

thanks but this doesnt work the way it should.I think i attached a wrong file. I have attached another to this message. How do i check that F3 is the next empty cell and then write to it? I want to be able to always check for the next empty column after column E.Test.xlsx (8.7 KB)