If you have changed your database password in ServerPilot, you will also need to change it in Drupal's code for your app to run correctly.
First, open your Drupal app's settings.php file, located at
apps/APPNAME/public/sites/default/settings.php
Then, scroll down until you see the line
$databases['default']['default'] = array (
Here you'll see where to edit your database credentials.