How to design copywriting on the keyboard for Android phones

What you are asking is how to design the characters on the keyboard. You can set the input method.

The characters on the keyboard can be set by the function of input method. Take sogou input method as an example. Click the keyboard icon to enter. There are six input methods, choose the one that suits you. You can set one-handed operation in the one-handed keyboard. Set the keyboard according to your own needs, and click Finish. Click skin settings to enter, then select your favorite skin, and click "Enable" to switch to the new skin.