EMUI allows for the screen to be resized at command to enable easy reachability of tough to reach menu buttons during one-handed operation.
To enable One Handed UI mode, go to Settings > Smart assistance > One-handed UI, then you can enable the one hand mode but before you jump into these features here are the following things you should know about.
If you are using gesture style, to enable Mini Screen View, you need to swipe up diagonally from either bottom-left or bottom-right to shrink the screen down into the corner and make those apps easier to reach with one finger. To exit one-handed mode just tap outside of the shrunken display.
If you are using the traditional three-key styled navigation, to enable Mini Screen View, you need to swipe left or right across the navigation bar. To exit one-handed mode, just tap the black area outside of the screen.