how to get into recovery mode

Follow these instructions:

If you can't update or restore your iPhone, iPad, or iPod touch - Apple Support

Hello,

To restart your iPad into recovery mode hold down the sleep/wake and home buttons at the same time. The screen should go black. Keep holding them until you see the Apple logo appear. Soon after you should see the iTunes icon and a lightning connector. You then can plug the iPad into a computer to have it recovered. You can install the latest iOS, restore from an iTunes backup, or wipe the device completely and reinstall the latest version of iOS. Note however, if Find My iPad was enabled on the device, it will still be. Even if you wipe the device Activation Lock will be enabled and you will need your Apple ID and password to use it. Otherwise the device is no more than a paperweight that omits light.