Attempt at installing TWRP on LG-V400, sort of bricked

I have an LG V400 which I successfully rooted using KingRoot. I installed Flashify on it and flashed a TWRP image from techbeasts.com. I then used Flashify's built in "Boot into Recovery" option. On boot,

Code:

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ERROR: Boot certification verify

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was written in small print at the top left corner of the tablet. It was stuck there for about 15 minutes, until I hard rebooted it and it came to the lock screen. However, I can not reset the tablet to factory defaults (it need to reboot to do that), nor do I have a backup image of the tablet before the failed installation. If I try to reboot the device, it shows the same error on boot until you hard reboot it. How can I get out of this? (preferably reset the tablet to factory defaults).