Updating the mysql database based on user input

I want to insert the selected status timestamps in the corresponding column which user has chosen from the menu.
Brief explanation
Start from the database i have created columns like snap below.
Initially user will insert the sonumber and status, Now i need database to update current time and date in the database, remaining column initialized to zero.
Next user will select update option, here user will enter so-number as well as new status(from dropdown). Now i need database to update the new status with current time and store in the particular status column.

Starting with insert page saved as "insert.html" and "insert.php" Respectively

<form id="form1" name="form1" method="post" action="insert.php" >
<p>
<lable>ENTER SO NUMBER</lable>
<input type="text"  name="soid" id="soid" maxlength="6" required>


<p>
<lable>SELECT DEPARTMENT</lable>
<select type="text"  name="dept" id="dept">

<option value="NGS Analysis">NGS Analysis</option>
<option value="E-Array">E-Array</option>
<option value="Micro-Array">Micro-Array</option>
<option value="NGS Data">NGS Data</option>


</select>
</p>

<p>
<lable>SELECT STATUS</lable>
<select type="text"  name="status" id="status">

<option value="Sample Recived">Sample Recived</option>
<option value="Mol Bio Extraction">Mol-Bio Extraction</option>
<option value="Extraction QC">Extraction QC</option>
<option value="Library Prep">Library Prep</option>
<option value="Library QC">Library QC</option>
<option value="Sequencing">Sequencing</option>
<option value="Data check">Data Check</option>
<option value="Re-Sequencing">RE-Sequencing</option>
<option value="QC Check">QC Check</option>
<option value="Analysis Started">Analysis Started</option>
<option value="Analysis Completed">Analysis Completed</option>
<option value="Report">Report</option>
<option value="Outbound">Outbound</option>
</select>
</p>



<p><button><img src="http://brandonmadeawebsite.com/images/art/icons/insert_icon.png"  height="50" />INSERT</button></p>
</form>

insert.php

<?php


 $so = $_POST['soid'];

 $dp = $_POST['dept'];

$servername = "localhost";
$username = "root";
$password = "";
$dbname = "status";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_errno) {
    printf("Connect failed: %s\n", $conn->connect_error);
    exit();
}
$result = mysqli_query($conn, "INSERT INTO $dbname.statusinfo (soid, dept ) VALUES ( '$so','$dp')") or die(mysqli_error($conn));
echo "Inserted sucessfully with So Number <u><b>$so</b></u> Corresponding Status is <u><b>$st</b></u>";


$conn->close();

?>  

Now below update script which is saved as "update.html","update.php" respectively

<form action="update.php" method="post" name="form2">
<p>
<lable>ENTER SO NUMBER</lable>
<input type="text"  name="soid" id="soid" required>

<p>
<lable>SELECT STATUS</lable>
<select type="text"  name="status" id="status">

<option value="Sample Recived">Sample Recived</option>
<option value="Mol Bio Extraction">Mol-Bio Extraction</option>
<option value="Extraction QC">Extraction QC</option>
<option value="Library Prep">Library Prep</option>
<option value="Library QC">Library QC</option>
<option value="Sequencing">Sequencing</option>
<option value="Data check">Data Check</option>
<option value="Re-Sequencing">RE-Sequencing</option>
<option value="QC Check">QC Check</option>
<option value="Analysis Started">Analysis Started</option>
<option value="Analysis Completed">Analysis Completed</option>
<option value="Report">Report</option>
<option value="Outbound">Outbound</option>


</select>
</p>

<p><button><img src="http://icons.iconarchive.com/icons/icons8/windows-8/32/User-Interface-Available-Updates-icon.png"  height="50" /> UPDATE</button></p>
</form>

update.php

<?php
 $so = $_POST['soid'];
 $st = $_POST['samplerecived'];
 $st1 = $_POST['molbioextraction'];
$servername = "localhost";
$username = "root";
$password = "";
$dbname = "status";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_errno) {
    printf("Connect failed: %s\n", $conn->connect_error);
    exit();
}
   switch ($st):

case $st:$result = mysqli_query($conn, "UPDATE statusinfo SET `samplerecived`= CURTIME()  WHERE soid='$so' ") or die(mysqli_error($conn));
    break;
case $st1:$result1 = mysqli_query($conn, "UPDATE statusinfo SET  `molbioextraction`= CURTIME() WHERE soid='$so' ") or die(mysqli_error($conn));
    break;
echo "Updated sucessfully with So Number $so Current Status is set to $st ";

  $conn->close();

   ?>

Kindly help me to do so, if you guys need any more information feel free to ask.
Thanks in advance