Hard Reset BLACKVIEW A9 Pro

First method:

Begin by holding the Power key for a few seconds to switch off the device.
After that press and push Volume Up and Power buttons together for a couple of seconds.
Release all keys when Boot Mode pops up.
Now choose "Recovery". Use Volume Up to navigate and Volume Down to accept it.
When the Andorid Robot appears press Volume Up and Power buttons again.
In Recovery Mode you have to select "wipe data/factory reset" by using Volume key and the Power key to accept it.
Then choose "yes" from the menu, and confirm with the Power button.
Finally select "reboot system now" by using the Power key.
Good job!