C Sharp for loop problem

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C#

I know that if we want to increase the index i into 1 every time in a for loop we write i++
But I want to increase i into 7 every time. I have given my code. Can anyone help me, please!!!

if (ddlMaintenPlan.SelectedItem.Text == "Weekly")
           {
               
               DateTime dtLastday = Convert.ToDateTime(dtpMaintenceEnd.Text.Trim());
               while (dsStartDate <= dtLastday)
               {
                   
                   for (int i = Convert.ToInt32(dsStartDate); i < Convert.ToInt32(dtLastday); i++)
                   {
                       dsStartDate = Convert.ToDateTime(Convert.ToInt32(dsStartDate) + Convert.ToInt32(i.ToString()));
                       DRLocal = DTLocal.NewRow();
                       DTLocal.Rows.Add(dsStartDate);
                   }
               }



           }