file1.php

<form action="file2.php" method="POST">
    <input type="type" name="info">
    <input type="submit" name="submit_from_form1" value="submit">
</form>

file2.php

if (isset($_POST['submit_from_form1'])) {
    $info = $_POST['info'];
} else {
    // in case user access file2.php directly then redirect back to file1.php
    exit(header('location: file1.php'));
}

<form action="file3.php" method="POST">
    <input type="text" name="something">
    <input type="text" name="info" value="<?php echo $info; ?>">
    <input type="submit" name="submit_from_form2" value="submit">
</form>

file3.php

if (isset($_POST['submit_from_form2'])) {
    $something = $_POST['something'];
    $info = $_POST['info'];
    // update your database
}