Button on iPad not working

Is there a specific physical button that doesn’t function? Some functions can be accessed using the Assistive Touch function. The iPad User Guide provides details:

Use AssistiveTouch on iPad - Apple Support

However, it is a common misconception that an iPad (or iPhone) can remain fully functional with damaged or defective physical buttons. 

Whilst Accessibility features (such as assistive touch) can be used to augment the User Interface, these features cannot be used as a substitute for physical button sequences that must be used to trigger system recovery actions. Sooner or later, you will encounter a situation from which you cannot recover.

If your iPad has any damaged/unresponsive physical buttons, until repaired, you will not be able to resolve many problems.

You may wish to consider repair or replacement of your iPad. You might consider a visit to the Genius Bar at your local Apple Store or Apple Authorised Service Provider (AASP) - where the technicians will be able to assess your iPad - and you will be able to explore your available options:

Genius Bar Reservation and Apple Support Options - Apple

click here ➜ Writing an effective Apple Support Communities Question - Apple Community

What button?

What happens when you press it?

What specific model?

Have you followed the suggestions in the support document you posted from?