How can save date from textbox to database using Entity Framework?

dtpGraduationYear is a TextBox that contains a date.
I want to save the date from the textbox to database using Entity Framework.

private void btnSaveAll_Click(object sender, EventArgs e)
{
    //
    // tab Education
    //         
    var Education = new database.tblEmployeeQualification
    {
        EmployeeCode = Convert.ToInt32(txtCode.Text),
        UniversitiyCode = string.IsNullOrEmpty(txtEdUniversitiesNo.Text) ? (byte?)null : Convert.ToByte(txtEdUniversitiesNo.Text), 
        FauculityCode = string.IsNullOrEmpty(txtEdFacultyNo.Text) ? (byte?)null : Convert.ToByte(txtEdFacultyNo.Text), 
        QualificationsCode = string.IsNullOrEmpty(txtEdQualificationNo.Text) ? (byte?)null : Convert.ToByte(txtEdQualificationNo.Text), 
        SpecializationCode = string.IsNullOrEmpty(txtEdSpecializationNo.Text) ? (byte?)null : Convert.ToByte(txtEdSpecializationNo.Text), 
        EductionGrade = string.IsNullOrEmpty(txtEdGradeNo.Text) ? (byte?)null : Convert.ToByte(txtEdGradeNo.Text), 
        QualificationsTypeCode = string.IsNullOrEmpty(txtQualificationTypeNo.Text) ? (byte?)null : Convert.ToByte(txtQualificationTypeNo.Text), 
        GraduationYear = dtpGraduationYear.ToString("dd/MM/yyyy"),
        Note = txtEdNote.Text,
    };

    db.tblEmployeeQualifications.AddOrUpdate(Education);
    db.SaveChanges();
}

Error is here
GraduationYear = dtpGraduationYear.ToString("dd/MM/yyyy"),
error:

> no overload for method 'tostring' takes 1 arguments

This is my model class:

public partial class tblEmployeeQualification
{
    public int EmployeeCode { get; set; }
    public Nullable<short> UniversitiyCode { get; set; }
    public Nullable<short> FauculityCode { get; set; }
    public Nullable<short> QualificationsCode { get; set; }
    public Nullable<short> SpecializationCode { get; set; }
    public Nullable<byte> EductionGrade { get; set; }
    public Nullable<byte> QualificationsTypeCode { get; set; }
    public Nullable<byte> MainEducationCode { get; set; }
    public Nullable<System.DateTime> GraduationYear { get; set; }
    public string Note { get; set; }
    
    public virtual tblEmployeeData tblEmployeeData { get; set; }
    public virtual tblEnglishLevel tblEnglishLevel { get; set; }
    public virtual tblFaculty tblFaculty { get; set; }
    public virtual tblMainEduaction tblMainEduaction { get; set; }
    public virtual tblQualification tblQualification { get; set; }
    public virtual tblQualificationType tblQualificationType { get; set; }
    public virtual tblSpecialization tblSpecialization { get; set; }
    public virtual tblUniversity tblUniversity { get; set; }
}

You can use:

GraduationYear = Convert.ToDateTime(dtpGraduationYear.Text.ToString());

The line with the error you said is here:

GraduationYear = dtpGraduationYear.ToString("dd/MM/yyyy")

dtpGraduationYear you said is a TextBox. As with all your other textboxes, you need to read the Text property. As the error says:

>no overload for method 'tostring' takes 1 arguments

That is, TextBox has a ToString() method, but it takes no arguments.

This is only half the answer though, your model expects GraduationDate to be Nullable<DateTime> - you'll need to convert the text to that type, probably using DateTime.Parse or DateTime.TryParse.