Download the official Lava V5 flash file, Stock ROM or Firmware.
Marshmallow update has been also released for Lava V5.
Lava V5 s210 20160823 (MarshMallow)
SP Flash Tool : Quick Points
Try to use Firmware Upgrade option to initialize Flashing.
While, loading Firmware in SP Flash tool.
Untick Preloader, which held responsible for Mobile life. If this file get corrupt, your Lava V5 will be dead.
Make sure to install Mtk driver to make communication between Mobile & PC (Flash tool)
While, installing Stock ROM. If the process get interrupted, it will result in Android logo with exclamation mark.
Gmail Unlock (FRP Lock):
You can use Miracle box with update version 2.27 or higher to unlock FRP directly.
Note: Lava V5 runs on Lollipop and Upgradeable to Marshmallow. If you are trying flashing to unlock/reset Gmail id. It will fail.