Drupal - Reset user password without using "Forgot password?"

It's easier these days:

$account = \Drupal::entityTypeManager()->getStorage('user')->load(1);
$account->setPassword('new password');
$account->save();

Alternately, since you seem to be running this as a standalone script, there is a Drush (9.x) command

drush user:password admin mynewpassword

For Drush 8.x and earlier::

drush user-password admin --password=newpass

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