I need to modify the value of a column using Epplus

Question

I need to modify the value of a column First I look for the column by its name, getting the index. I would like to see how I can modify the value of that column based on its ID, or on the contrary, on its range

public static class EpPlusExtensionMethods
{ 
    public static int GetColumnByName(this ExcelWorksheet ws, string columnName)
    {
        if (ws == null) throw new ArgumentNullException(nameof(ws));
        return ws.Cells["1:1"].First(c => c.Value.ToString() == columnName).Start.Column;
    }
}

int columnId = ws.GetColumnByName("Birthdate");