"Congratulate in public, assess in private"
Think about how you would like to be told the things you need to improve. Read this article if you need help expressing a criticism.
If you have the complaint is towards a specific person, never do it publicly and anonymously in Happyforce, instead do the following:
Talk to that person directly.
If you can not talk to him/her because it is not possible, you do not dare, you do not know what to say or how to do it, talk to the peoples department of your company. For these things, they know how to help you and guide you
If you are not comfortable doing it personally, you can send a private and anonymous comment through Happyforce. For this, choose the band-aid and make sure that the "Private Comment" is marked