Hi Patrick,
Thank you for contacting us. Due to the way Face ID works, there is no way to recover passwords for certain apps. When you set up Face ID unlock, the password you enter is encrypted and stored in iOS's "Secure Enclave." That data cannot be retrieved, as that is the main point of storing data in the "Secure Enclave." Also, after you have changed the Face ID information, all data that was stored in the "Secure Enclave" is dropped, so it is no longer available. In the end, the only way to get into mSecure after changes are made to the Face ID Settings is to enter your account password manually, and then set up Face ID unlock again in the app's Settings.
Patrick