If you think that a certain chat violates our Guidelines, best way to help us identifying it is to simply report the conversation in the app.
Open the respective chat in the apps chat-tab.
Click on the ••• menu and select Report & block user.
After reporting the selected chat, it will automatically be removed from your chat-tab so that you no longer have access to it.
If you believe that the content in question is legally relevant, contact your local police station and report the matter to them. In such cases, it is advisable not to report the chat in question yet in order to retain access to the relevant messages.