In addition to the way @Pablito said u can try this way too
You can try something like this
Read range to read the excel and store in datatable dt1
Use assign activitiy to assign as below
day_1= Now.ToString(“dd”)
Use invoke code with code type as c# with passing dt1 as in/out argument and day_1 as input argument with below code
dt1.Columns.Add(day_1)
Next use write range to write the updated dt1
Hope it helps you
Regards
Nived N
Happy Automation