我做错了什么？ （PHP准备声明）

First time I'm using a prepare function, and I got it to partially work. Basically, I'm copying user passwords from one database to another (part of a WordPress plugin I'm making to transfer users). The code runs and does exactly what I want, but only for the first user it finds in the wp_users table. I need it to continue running for all the users in that table so they all get their passwords transfered. This is the code I wrote below:

For getting the user password from the original database (Basically, this finds the passwords for all the users and puts them in an array. I'm posting this code just for context. This code works perfectly fine):

$i = 0;
//set $user_count-1 because $i needs to start at 0 to represent the indexes and it also prevents the statement from being looped an extra time.
while($i <= $user_count-1) {
if($result = $conn->query("SELECT * FROM wp_users")) {
    if($count = $result->num_rows) {
        //echo $count . ' users found.';

        while($row = $result->fetch_object()) {
            $user_password[] = $row->user_pass;
        }
    }  
$i++; 
}

To retrieve the index values (This is the code I'm using to actually retrieve those index values and put them in the sql query. Like I said, it works fine for the first user, but not the rest of the users):

$stmt = $conn->prepare("UPDATE `wp_plugin_development`.`wp_users` SET `user_pass` = ? WHERE `wp_users`.`user_login` = ?");
$stmt->bind_param('ss', $user_password[$i], $user_login[$i]);
$stmt->execute();

I'm thinking maybe the syntax is wrong? I don't know. I hope I made my question clear enough. Thanks for any help!

I figured it out!

Originally, I put the code to prepare the statement and the code to execute it together. prepare and bind_param needs to be placed before $i auto-increments. The execute needs to be placed after $i auto-increments. Here's the code that works:

$i = 0;
//using $user_count-1 because $i needs to start at 0 to represent the indexes and it also prevents the statement from being looped an extra time.
while($i <= $user_count-1) {
if($result = $conn->query("SELECT * FROM wp_users")) {
    if($count = $result->num_rows) {
        //echo $count . ' users found.';

        while($row = $result->fetch_object()) {
            $user_password[] = $row->user_pass;
$stmt = $conn->prepare("UPDATE `wp_plugin_development`.`wp_users` SET `user_pass` = ? WHERE `user_login` = ?");
$stmt->bind_param('ss', $user_password[$i], $user_login[$i]);
        }
    }  
$i++; 
if(!$stmt->execute()){trigger_error("there was an error....".$conn->error, E_USER_WARNING);}
}

Thank you everyone for your input!