On the change password page, if user enter blank password fields, it will show the message "Please correct the errors highlighted below and try again." (id="rwmb-validation-message")
You can try to use the filter hook rwmb_validation_message_string to customize the validation message. The code is located in the file /wp-content/plugins/meta-box-aio/vendor/meta-box/meta-box/inc/validation.php
There isn't a list of all filter/action hooks of Meta Box plugins. Because some of them are rarely used, we have a list of filter/action hooks that are usually used. Please check the documentation https://docs.metabox.io/category/references/