How can I save data from custom datagridview to database

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VB

SQL

Hi guys
I have a DataGridView with Header Colunms days of month.
Here is an image
https://ibb.co/b3JPRXN

I use this code to load data from database

<pre> Private Sub fill_plan()
        EmployeeGridView.Rows.Clear()
        Try
            Dim i As Integer = 0
            con.Open()
            Dim query As String = "SELECT UnitID,Unit,Udate,State FROM Units where Month(Udate) =" & cmbMonth.SelectedIndex + 1 & ""
            cmd = New SqlCommand(query, con)
            myDR = cmd.ExecuteReader
            If myDR.HasRows Then
                While myDR.Read
                    EmployeeGridView.Rows.Add()
                    EmployeeGridView.Rows(i).Cells(0).Value = myDR.GetInt32(myDR.GetOrdinal("UnitID"))
                    EmployeeGridView.Rows(i).Cells(1).Value = myDR.GetString(myDR.GetOrdinal("Unit"))
                    Dim myday As Integer = DatePart(DateInterval.Day, myDR.GetValue(myDR.GetOrdinal("Udate")))
                    EmployeeGridView.Rows(i).Cells(myday + 1).Value = myDR.GetString(myDR.GetOrdinal("State"))
                    i = i + 1
                End While
            End If
            myDR.Close()
            con.Close()
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "Σφάλμα")
        End Try
    End Sub

What I have tried:

Private Sub btnAdd_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnAdd.Click
        Try
            con.Open()
            cmd.CommandText = "INSERT INTO Units(Unit,Udate,State) VALUES(@unit,@udate,@state)"
            cmd.Parameters.Add("@unit", SqlDbType.NVarChar, 255)
            cmd.Parameters.Add("@udate", SqlDbType.DateTime)
            cmd.Parameters.Add("@state", SqlDbType.NVarChar, 10)
            For Each row As DataGridViewRow In EmployeeGridView.Rows
                For i = 1 To 31
                    'Dim myday As Integer = DatePart(DateInterval.Day, CDate("Udate"))
                    cmd.Parameters("@unit").Value = EmployeeGridView(1, EmployeeGridView.CurrentCell.RowIndex).Value.ToString()
                    cmd.Parameters("@udate").Value = 
                    cmd.Parameters("@state").Value =
                    cmd.ExecuteNonQuery()
                Next
            Next
            con.Close()
        Catch ex As Exception
            MsgBox(ex.Message, MsgBoxStyle.Critical, "Σφάλμα")
        End Try

    End Sub

The parameters are empty because i don't know what to write

Thanks in advance