First of all, you should check whether you can submit your information via the ombudsman's office. A report should only be submitted to an external reporting office if it is not possible or reasonable to deal with the report in the internal whistleblower system or if such a report has proved unsuccessful or futile.
The reporting office of the Federal Bureau of Anti-Corruption (BAK) is available to you as an external office (https://www.bkms-system.net/BAK).