Check which devices are signed in with your Apple ID by going to Settings > [your name]. If you see a device you don’t recognize, tap the device name and select Remove from Account.
Sign in to appleid.apple.com with your Apple ID and review all the personal and security information in your account to see if there is any information that someone else has added. Make sure all your information is up to date. If you have two-factor authentication turned on, review trusted devices for any devices that you do not recognize. If your account doesn’t use two-factor authentication, turn it on now.
Review the installed apps on your device and look for apps you don’t recognize or don’t remember installing. You can look up any apps you find in the App Store to see what their purpose is.
Mobile Device Management (MDM) profiles are typically installed by employers, schools, or other official organizations, and allow additional privilege and access to a device. Look for an unknown MDM profile on your iPhone, iPad, or iPod touch in Settings > General > Profiles & Device Management. If you don’t see this option in Settings, your device doesn’t have any profiles installed.
Review additional checklists if you want to stop sharing with someone you previously shared with and if you want to make sure no one else can see your location.
For even more detailed information, you can download and read Device and Data Access when Personal Safety is At Risk.