Hello guys. I am learning C# and I have been unable to get the delete function to work in my code. What could I be doing wrong?

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;
using System.Data.SqlClient;
namespace Point_of_sale
{
    public partial class manageUsers : Form
    {
        public manageUsers()
        {
            InitializeComponent();
        }
        SqlConnection Conn = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\GARNET6\Documents\inventorydb.mdf;Integrated Security=True;Connect Timeout=30");
     
        private void label1_Click(object sender, EventArgs e)
        {
            Application.Exit();

        }
        void populate()
        {
            try
            {
               Conn.Open();
                string Myquerry = "select * from UserTb1";
                SqlDataAdapter da = new SqlDataAdapter(Myquerry, Conn);
                SqlCommandBuilder builder =  new SqlCommandBuilder(da);
                var ds = new DataSet();
                da.Fill(ds);
                UsersGV.DataSource = ds.Tables[0];
                Conn.Close();
                

            }
            catch
            {

            }
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
           
            try
            {
                Conn.Open();
                SqlCommand cmd = new SqlCommand("insert into UserTb1 values('" + UnameTb.Text + "', '" + FnameTb.Text + "', '" + PasswordTb.Text + "', '" + PhoneTb.Text + "')", Conn);
                cmd.ExecuteNonQuery();
                MessageBox.Show("User sucessfully added");
                Conn.Close();
                populate();


            }

            catch
            {

            }
        }

        private void label2_Click(object sender, EventArgs e)
        {

        }

        private void label5_Click(object sender, EventArgs e)
        {

        }

        private void richTextBox2_TextChanged(object sender, EventArgs e)
        {
          
        }

        private void dataGridView1_CellContentClick(object sender, DataGridViewCellEventArgs e)
        {
            UnameTb.Text = UsersGV.SelectedRows[0].Cells[0].Value.ToString();
            FnameTb.Text = UsersGV.SelectedRows[0].Cells[1].Value.ToString();
            PasswordTb.Text = UsersGV.SelectedRows[0].Cells[2].Value.ToString();
            PhoneTb.Text = UsersGV.SelectedRows[0].Cells[3].Value.ToString();


        }

        private void label6_Click(object sender, EventArgs e)
        {
            Application.Exit();
        }

        private void ManageUsers_Load(object sender, EventArgs e)
        {
            populate();
        }

        private void button3_Click(object sender, EventArgs e)
        {
            if (PhoneTb.Text == "")
            {
                MessageBox.Show("Proceed to delete?");

            }
            else
            {
                Conn.Open();
                string myquery = "delete from UserTb1 where Upassword '"+PhoneTb.Text+"'";
                SqlCommand cmd = new SqlCommand(myquery, Conn);
                cmd.ExecuteNonQuery();
                MessageBox.Show("User successfully deleted");
                Conn.Close();
                populate();
            }
        }


    }
}