SQL query: updating/inserting data in C# application : I created 3 tables

    Clients: Client_ID, Client_Name, Client_Status,
    Employees:Emp_ID, Emp_Name, Emp_Role  
    EmpJobs:EmpJob_ID, Emp_ID, Client_ID, Hours_Spent, Job_Date 

 now I need a function where the user enters data (Hours_Spent, Job_Date) to EmpJobs based on Client_Name and Emp_Name. This is what I tried 

    string constring = "Data Source=baker-pc;Initial Catalog=BakodahDB;Integrated Security=True";
                string sqlQuery = (@"INSERT INTO EmpJobs (Hours_Spent, Job_Date)
                    values (@Hours_Spent,@Job_Date) 
                    INNER JOIN Clients
                    ON EmpJobs.Client_ID=Clients.Client_ID
                    INNER JOIN Employees
                    ON EmpJobs.Emp_ID=Employees.Emp_ID
                    WHERE Clients.Client_Name=@Client_Name AND Employees.Emp_Name=@Emp_Name");
    
                    SqlConnection conDataBase = new SqlConnection(constring);
                    SqlCommand sqlCommand = new SqlCommand(sqlQuery, conDataBase);
                    conDataBase.Open();
                    sqlCommand.CommandText = sqlQuery;
                    sqlCommand.Parameters.Add("@Hours_Spent",SqlDbType.Int).Value = comboBox3.SelectedItem;
                    sqlCommand.Parameters.Add("@Job_Date",SqlDbType.Date).Value = Convert.ToDateTime(dateTimePicker1.Text);
                    sqlCommand.Parameters.Add("@Client_Name", SqlDbType.VarChar).Value = comboBox1.SelectedItem;
                    sqlCommand.Parameters.Add("@Emp_Name", SqlDbType.VarChar).Value = comboBox2.SelectedItem;
                    sqlCommand.ExecuteNonQuery();
                    conDataBase.Close();
                    MessageBox.Show("Saved!");

What am i doing wrong? what's the correct way to do it?