Reset security questions - Try Apple's iForgot service. If it says they don't have sufficient information, then you need to contact Apple's account security team. To reach it, click here and select a method; If you can't use any of the forms listed, fill out and submit this form.
See if you're already signed in with your Apple ID
On your iPhone, iPad, or iPod touch. Tap Settings, then tap [your name].
On your Mac. Choose Apple menu > System Preferences, then click Apple ID.
On your PC. Open iCloud for Windows, then look for your Apple ID under your name.
If you lost / can't reach the trusted device or phone number associated with your Apple ID
Go to your Apple ID account page and enter your Apple ID and password.
On the Verify Your Identity screen, select "Can't access your trusted devices?"
In the pop-up window, enter your Recovery Key.
For more Info - https://www.wikicue.com/iforgot-apple-com-reset-my-security-questions/