// Carrega mac do banco
$sqlMac = "SELECT idmacmiguel, nome FROM macmiguel ORDER BY nome";
$stmtMac = $conn->query($sqlMac);
$placasmac = $stmtMac->fetchAll(PDO::FETCH_ASSOC);


// Seleciona mac do banco
 <label>Mac:</label>
    <select name="idmacmiguel" required>
        <option value="">Selecione...</option>
        <?php foreach ($placasmac as $cat): ?>
            <option value="<?= $cat['idmacmiguel'] ?>">
                <?= htmlspecialchars($cat['idmacmiguel']) ?>
            </option>
        <?php endforeach; ?>
    </select>
    
//Ajustar o formulário:
           <label> = Data fim: " . date('d/m/Y H:i:s', strtotime($row[6])) . "</label>
            <label>MAC: " . htmlspecialchars($row[7]) . "</label><br>
            <!-- Formulário UPDATE -->
            <form method='post' action='' style='display:inline;'>
                <input type='hidden' name='acao' value='update'>
                <input type='hidden' name='idaltera' value='$row[0]'>
                <label>Led R:<input type='number' name='novoLedr' style='width: 50px;' value='$row[1]'>    
                <button type='submit'>Atualizar</button>
            </form>