Citizens Bank, How To Report?!
Citizens Bank, National Association, is regulated by The FDIC.
Here is a link to file with them, you may file anonymously as well.
https://ask.fdic.gov/fdicinformationandsupportcenter/s/?language=en_US
As far as their broken mobile app goes...
https://play.google.com/store/apps/details?id=com.citizensbank.androidapp
Here is a link on how to flag it via Google Play Store.