Tap 'Tools' > 'About' and tap 5 times on the firmware version number. It will then inform you that 'servo calibration mode' is activated. Tap the back arrow, then tap 'settings', scroll down to the second page and tap 'Servo Calibration'
Note: To disable servo calibration mode, simply turn the printer off for a few minutes.
Now that you are in Servo mode, you'll notice a sliding switch icon. This simply puts the levelling arm down, or up. Tap it a few times and you'll both hear, and see the levelling arm pop down and up.
Under the sliding switch icon is a number. This number tells the printer how far it needs to move the levelling arm, in order for it to be vertical.
If the levelling arm doesn't move far enough to be vertical, then you will need to increase that number slightly. Then just tap the sliding icon twice to test it. Repeat as needed.
If the levelling arm moves too far and you can hear or see it strain sideways, then you will need to decrease the number slightly. Then just tap the sliding icon twice to test it. Repeat as needed.