How to avoid replication of data copied from datagridview to database?

I have a difficulty, I have code that allows to capture all information from the datagridview and send in the database. Whenever I have execute the code it replicates in the database, and I do not know how to do it.

public void GetAllUserID()
      {
              SqlConnection con = new System.Data.SqlClient.SqlConnection();
              con = new System.Data.SqlClient.SqlConnection();
              //con.ConnectionString = "";
              con.ConnectionString = @"Integrated Security=SSPI;Persist Security Info=False;Initial Catalog=DBTESTE;Data Source=PD\PRIMAVERA";
              con.Open();
              SqlDataAdapter da = new SqlDataAdapter();
              for (int i = 0; i <= dgvRecords.Rows.Count - 1; i++)
              {

                  string insertData = "insert into tbAlluserid (MachineNumber, EnrollNumber, BackupNumber) values (@MachineNumber, @EnrollNumber, @BackupNumber)";
                  SqlCommand cmd = new SqlCommand(insertData, con);
                  cmd.Parameters.AddWithValue("@MachineNumber", dgvRecords.Rows[i].Cells[0].Value);
                  cmd.Parameters.AddWithValue("@EnrollNumber", dgvRecords.Rows[i].Cells[1].Value);
                  cmd.Parameters.AddWithValue("@BackupNumber", dgvRecords.Rows[i].Cells[2].Value);
                  da.InsertCommand = cmd;
                  cmd.ExecuteNonQuery();

              }
          }

I tried, the method that allows deleting the table, but not the desired one