I how do I restore original keyboard on iPad air2?

See >>> Split and move the keyboard on your iPad – Apple Support

To easily return the Split Keyboard to the full on-screen keyboard, you can either use two fingers (one on each of the two half-keyboards) and swipe the two halves together - or touch-and-hold the “keyboard” key, then slide your finger to the Merge & Dock option and release.

I hope this information and guidance proves to be helpful in resolving your difficulties.

See this article for help:--> Split and move the keyboard on your iPad - Apple Support

Regards

Giulio