Check Family Sharing settings by going to Settings > [your name]. If you’re in a family, the names of the family members are visible. If you’re part of a family, you can remove yourself from the family group as long as the account lists your age as over 13. If you’re the family organizer, you can remove anyone over the age of 13 from the family.
In the Find My app, select the People tab to see with whom you share your location. Tap a person and tap Stop Sharing My Location, or to stop sharing with everyone, turn off Share My Location in the Me tab.
In the Photos app, go to Albums and then go to Shared Albums. Select a shared album and tap People to see the owner of the shared album and with whom the album is shared. If you’re the album owner, tap the name of a subscriber for the option to remove them. If you’re a subscriber, select Unsubscribe from the bottom of the screen. You can also delete any photos that you shared.
In the Calendar app, select Calendars. Select a shared calendar and tap Info to see with whom the album is shared. If you’re the calendar owner, tap the name of the subscriber for the option to remove them. If you're a subscriber, you can tap Delete Calendar from the bottom of the screen.
If you have an Apple Watch and shared your Activity rings with someone, you can choose to stop sharing. In the Fitness app on your iPhone, tap the Sharing tab. Tap the person icon to see who you share with, click on the person's name and select either Remove Friend or Hide my Activity.
You can choose to share information with others through third-party apps as well. Review the apps that you installed on your device to see if any of them are sharing information, and follow their instructions to stop sharing. You can also delete the app.
If you’re not running the latest version of iOS and have concerns that someone else may have had physical access to your device, or if someone else set your device up for you, you can back up the information from your device and restore it to factory settings. Learn how to back up your iPhone, iPad, and iPod touch and how to erase your iPhone, iPad, or iPod touch.
Review additional checklists if you want to make sure no one else can see your location and if you want to see if anyone else has access to your device or accounts.
For even more detailed information, you can download and read Device and Data Access when Personal Safety is At Risk.