1. In the Instagram app, click on your username.
2. Select "Add account".
3. Click on the "Log in to an existing account" button.
4. Next, "Switch accounts".
5. Select the "Get help logging in"link.
6. Enter the username of the suspicious account.
7. Click "Next".
8. Click "Need more help?".
The window that opens will display the first and last two digits of the phone number, as well as the first and last letters of the linked emails to the account.
Thus, if this is a person close to you and you know his email or phone number, you can compare this one and understand whether it is him.
If desired, you can separately click on the "Send email" and "Send SMS" buttons. In the opened window will be displayed as part of the mail and telephone respectively.
Note: The names of the items and their locations may differ depending on the operating system and the version of the application.