Delete items in cart after user submit receipt

Question

What i want to do is, after user submit the receipt(image) the items in their cart will be deleted.

How do i combine the queries in one sql statement?

$stmt = $conn->prepare("DELETE FROM cart WHERE user_id=:user_id");

But how do i combine

<?php
    try{ 
        include 'includes/session.php';
        $conn = $pdo->open();
    } catch(PDOException $e){ 
        die("ERROR: Could not connect. ". $e->getMessage()); 
    } 

    if(isset($_POST['resit_submit'])){
        try{ 
            $sales_date = date('Y-m-d');
            $set='PR123456789';
            $pay_id=substr(str_shuffle($set), 0, 12);

            $stmt = $conn->prepare("UPDATE sales 
                SET sales_date=:sales_date, payment_id=:payment_id 
                WHERE user_id=:user_id");

            $stmt->execute([
                'sales_date'=>$sales_date, 
                'payment_id'=>$pay_id, 
                'user_id'=>$_SESSION['user']
            ]);
        } catch(PDOException $e){ 
            die("ERROR: Could not able to execute . ". $e->getMessage()); 
        } 

        $pdo->close();
?>