Sure, you can tell users the feature exists - in a place where showing it's available is relevant.
Changing pincode usually resides somewhere in settings, so show it's available within the settings page overview. If it's something that's rarely used - make sure you adhere to that hierarchy and don't place it at the top. This way you're not hiding its existence, nor taking away space for features that are used more often.
Users that are looking for an obscure feature will imagine under which main topic they could logically find this, and then go look for it. If your application structure is sound, they will find it intuitively. If you have a menu item called dashboard, or transactions, they will go look there for a reporting feature.
If your users are mainly using what you already push as main features - then it sounds like your application is doing what it should be doing. If they're complaining why you haven't added certain features yet, when it is in fact available, then you should look at changing the hierarchy and visibility of features. Then it is clear that your layout structure is making things hard to find.
Actions/features that are used a lot should be easy to see and navigate to, things that are used sparingly or are considered advanced can be placed deeper within the hierarchy.