My ipad mini has been restarted. I totally forgot the apple id and the password. How can i change or open the activation lock if i forgot everything. Is there any possible way?

The best way is to reset the information:

If you forgot your Apple ID (Hint: Usually this is the current email address)

https://support.apple.com/HT201354

If you forgot your Apple ID password - https://support.apple.com/HT201487

What to do after [or before] you change your Apple ID email address or password - https://support.apple.com/HT204071

If you still need help:

Contact Apple for help with Apple ID account security "This article provides country-specific Apple Support contact information for customers seeking help with their Apple ID password or other security-related issues."

https://support.apple.com/HT204169

or

Contact Apple for support and service - "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232

Now you can remove the activation lock. This may be the best way in your situation:

iCloud: Remove your device from Find My iPhone - http://support.apple.com/kb/PH2702

"If you’re no longer using an iOS device, an Apple Watch, AirPods, or a Mac, you can remove it from Find My iPhone using Find My iPhone on iCloud.com or your device. When you remove a device, it’s removed from your Find My iPhone Devices list, and if your device has iOS 7 or later, Activation Lock is also turned off."