If you would like to reset the password for your WordPress.com account in the app, enter your email address, then click the Get a login link by email option to receive a magic link in your email that will log you in when you click it.
Or you can click on the Reset your password option.
You can also reset your password from a browser here.
If you are referring to a WordPress.org (self-hosted) account you can follow the steps on this link:
