I need to put it in recovery mode, how?

These support pages outline the available methods to restore an iPad - utilising recovery mode - 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

If you can't update or restore your iPad - Apple Support

You’ll need access to either a PC (with iTunes 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.

Getting into it differs from iPad models. Check out this guide called If you can't update or restore your iPad - Apple Support