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. Until repaired, you will not be able to resolve a locked-out (disabled) iPad - or reset a forgotten device passcode.
iPad Repair & Service - Apple Support
If your iPd won’t turn-on using the top (Sleep/Wake) button, connect your iPad to its Power Adapter and allow the iPad to charge. When/if sufficiently charged, the iPad will automatically turn-on.
You description suggests that you iPad must be restored:
If you see the Restore screen on your iPhone, iPad, or iPod touch - Apple Support
These support pages outline the available methods to restore an iPad - either from a backup, or to Factory Settings:
Restore your iPhone, iPad or iPod touch from a backup – Apple Support
Restore your iPhone, iPad or iPod to factory settings – Apple Support
Restore all content to iPad from a backup - Apple Support
You’ll need access to either a Windows PC (with iTunes for Windows installed) or a Mac (with iTunes or Finder - as appropriate for the installed version of macOS).
Download and use iTunes for Windows – Apple Support
Update to the latest version of iTunes – Apple Support
Use of a PC or Mac computer is unavoidable. If you don’t have access to a suitable computer of your own, that of a helpful friend or family member will suffice. Alternatively, the technicians at the Genius Bar of your local Apple Store or Apple Authorised Service Provider (AASP) will be delighted to assist.
Genius Bar Reservation and Apple Support Options - Apple
