If someone pretending to be you then you can report that profile by checking "Spam or fraud" or by checking "Other reason" to describe the reason why are you reporting that profile.
If someone created a profile that you manage, you can simply submit a request for managing by clicking on "Submit a request for managing" button on that profile. If the user who created that profile accepts your request then you will be a manager too. But if you think that you're the only one manager of that profile, you can report that profile and we will do a deep check.
In both cases maybe we will ask you for your ID to identify you as a real person who owns that profile or ID of the profile which you want to manage.
If your profile is already verified then you have an advantage in proving ownership of profiles.
Read How can I get a verified badge on my profile for more information.