The iPhone Keyboard page of the Settings app has all the options you need to add and configure a new keyboard. After adding one, switch to it by tapping the Globe icon near the space bar.
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Open the Keyboard Settings
Open the Settings app to the General section and tap Keyboard.
Tap Keyboards to see the list of installed keyboards. The number on the Keyboards line shows how many keyboards you have installed.
Tap Add New Keyboard to see the keyboards available for installation.
Add a Built-In Keyboard
Choose a keyboard from the list to add it. Pick from the Suggested Keyboards section or scroll down to see all available keyboards. Some languages, such as English and Japanese, offer multiple layouts after you select them.
Add a Keyboard From an App
If you've downloaded a keyboard app and opened it on the home screen, you'll see it listed in the Third-Party Keyboards section below the suggested keyboards. Tap one to install it.
Switch Active Keyboards
After adding at least one extra keyboard, you'll see a globe icon on the keyboard whenever you type. Tap the globe to cycle through the installed keyboards. Tap and hold the icon to pick a specific keyboard from a list.