First, turn the device off. To do it press and hold the Power button, then tap the Power off on the screen.
Wait until the device turns off, then press and hold the Power button +Volume Down button. Release both buttons when the MIONE logo appears on the screen.
Now you should be in the Recovery menu. Use the Volume buttons to navigate through the menu.
Afterward, scroll down and select Wipe data/Factory data reset and press the Power button to continue.
Then scroll down to Yes and press the Power button to confirm.
After the process is complete, select the Reboot system now and press the Power button to confirm.