how to reset security questions if iPhone is disabled

It isn't clear to me if you are attempting to deal with two issues or one, but the following may help:

To reset security questions, see: If you forgot the answers to your Apple ID security questions - Apple Support

Note that it can be done from a computer. If you cannot reset them, contact Apple: Contact Apple for help with Apple ID account security - Apple Support

For a disabled phone, see 3 methods in If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support