The configuration of a change password page is very simple. You select a database connection among the available ones and an HQL query to execute on that connection. The query should select a single record, representing the user changing his/her password. Typically, the query will be filtered by the id of the user currently logged in, as shown in the picture.

Once you write a valid query and save the configuration, the property field becomes a selection box: select the property of the entity returned by the query that will contain the password.