simply create a page with a form to make the changes:
<form method="post" action="update.php">
<select name="availabillity">
<option>available</option>
<option>not available</option>
</select>
<input type="text" name="price">
<button type="submit">Submit</button>
</form>
In update.php
do something like this:
$new_price = $_POST['price'];
$availabillity = $_POST['availabillity'];
Then you simply run a new mysql query to update the data in the table:
"UPDATE YOURTABLE SET price = $new_price, availabillity = '".$availabillity."' WHERE id = yourid"
For more information on how to handle a form look here: Form handling in php
How to UPDATE data in mysql tables.
This is just example code to give you a hint.
Hope this helps you to get started.