The keyboard switching method in iOS has always left a lot to be desired. Get into the little shift key
Keyswipe (iOS eleven) - a new free jailbreak tweak thatallows you to switch keyboards with one swipe (up or down) on the keyboard. With it, you no longer have to find the little button on the keyboard with difficulty. Initially, this tweak was released in 2015, but it was optimized for iOS 11 just now.
KeySwipe (iOS 11) adds a section in Settings, where you can enable and disable it:
No options need to be configured, so using a tweak is very easy. If you want to install KeySwipe (iOS 11), you can download it from Julio Verne's beta repository in Cydia.