Each game is made by one person. Going straight to them is faster than anything else.
Post it in the comments on that game's page, or in the developer's Discord. Either works, but please include:
Before reporting, check you are on the latest build — a good share of reports are already fixed.
Every comment has a report button. Reports go to the developers, who review and remove anything that breaks the rules on conduct.
For copyright specifically, read the takedown policy first — a notice missing any of the listed details cannot be acted on.
.exe and .apk files trigger false
positives because they do not come from an app store. There is nothing we can change on our end.