For eu users : https://competition-policy.ec.europa.eu/antitrust/procedures/complaints_en
However not sure how it works, if you need to be directly affected as a company of user, or if you need to be a citizen to file a complaint.
I don't have the necessary detail and information to be able to file the complaint.
If you give the detail on how it works and why it affects competition I may be able to file a complaint.
Howerver from what I saw in news the EU and US are already collaborating in an investigation against Google. Not sure if it's true, current and on what exactly.