After click the edit button need to show the data in the textbox.

create table TblStaffdetails
(
Id int primary key identity(1,1),
StaffName varchar(40),
Designation varchar(40)
)

<form id="form1" runat="server">
    
        <table>
            <tr>
                <td>
                    Name
                </td>
                <td>
                    <asp:TextBox ID="TxtName" runat="server"></asp:TextBox>
                </td>
            </tr>

            <tr>
                <td>
                    Designation
                </td>
                <td>
                    <asp:TextBox ID="TxtDesignation" runat="server"></asp:TextBox>
                </td>
            </tr>

            <tr>
                <td>
                   <asp:Button ID="Save" runat="server" Text="Save" OnClick="Save_Click" />
                </td>
                <td>
                   <asp:Button ID="Edit" runat="server" Text="Edit" OnClick="Edit_Click" />
                </td>
            </tr>
            
        </table>
        <asp:Label ID="lblMessage" runat="server"></asp:Label>

    </form>

SqlConnection sqlcon = new SqlConnection("Data Source=JESUS-PC;Initial Catalog=userdb;Integrated Security=True");
        protected void Page_Load(object sender, EventArgs e)
        {

        }

        protected void Save_Click(object sender, EventArgs e)
        {
            sqlcon.Open();
            SqlCommand sqlcmd = new SqlCommand("Insert into TblStaffdetails values('"+ TxtName.Text +"','"+ TxtDesignation.Text +"')", sqlcon);
            sqlcmd.ExecuteNonQuery();
            TxtName.Text = "";
            TxtDesignation.Text = "";
            lblMessage.Text = "Saved Data!....";
        }

        protected void Edit_Click(object sender, EventArgs e)
        {
                DataTable Dt = new DataTable();
                sqlcon.Open();
                SqlDataAdapter sqlcmd = new SqlDataAdapter("Select top 1 * from TblStaffdetails order by id desc", sqlcon);
                sqlcmd.Fill(Dt);
                if (Dt.Rows.Count > 0)
                {
                    TxtDesignation.Text = Dt.DefaultView[0]["Designation"].ToString();
                    TxtName.Text = Dt.DefaultView[0]["StaffName"].ToString();
                }
            

        }

 protected void Edit_Click(object sender, EventArgs e)
        {
            if (TxtDesignation.Text == "" && TxtName.Text == "")
            {
                DataTable Dt = new DataTable();
                sqlcon.Open();
                SqlDataAdapter sqlcmd = new SqlDataAdapter("Select top 1 * from TblStaffdetails order by id desc", sqlcon);
                sqlcmd.Fill(Dt);
                if (Dt.Rows.Count > 0)
                {
                    TxtDesignation.Text = Dt.DefaultView[0]["Designation"].ToString();
                    TxtName.Text = Dt.DefaultView[0]["StaffName"].ToString();
                    Session["id"] = Convert.ToInt32(Dt.DefaultView[0]["Id"]);
                }
            }

            else
            {
                sqlcon.Open();
                SqlCommand sqlcmd = new SqlCommand("Update  TblStaffdetails set StaffName='" + TxtName.Text + "' where Id=" + Convert.ToInt32(Session["id"]) + "", sqlcon);
                sqlcmd.ExecuteNonQuery();
            }
        }

PageLoad

lbl.Text="text";
txt1.Text="text"; //by default textbox should be visible false

Edit button
lbl.Visible=false;
txt1.Visible=true;