Hello @glamglowing16
I assume you are using the WordPress mobile app to manage a self-hosted WordPress site, and not one hosted on WordPress.com?
To implement custom post types on a self-hosted site, you either have to create them yourself using PHP and the register_post_type function, or there are plugins that you can install on your WordPress site, that will allow you to create custom post types.
You can find them by searching the plugin repository here for the keywords custom post types
https://ww.wp.xz.cn/plugins/search/custom+post+types/
If I understand the question correctly, the OP is looking for custom post type support within the app rather than how to create them on a website.
Unfortunately, CPTs are not currently supported in the app. I have looked for the iOS app repo on GitHub to log a feature request and haven’t found one. The best workaround I can point you to is using a mobile browser.
The best place to submit feature requests depends on which device you are using. There are different Github Issue Trackers for the WordPress iOS app and WordPress Android app.