This option should be present on all Vivo phones. To turn it off:
Go to Settings → More settings
Tap on Applications
Find your application and turn on Autostart toggle
For Funtouch OS 2.6 and lower version:
Go to iManager → App manager
Tap on Autostart manager
Turn on the app switch
Lock the app in taskbar
Apps locked in the taskbar are safe from getting terminated when they run on the background.
Swipe up in your home screen while the app is open in background, and swipe the app icon down.
Tap the lock icon.
Done - now the app is locked in the taskbar.
Allow the app to keep running even during high power consumption
Go to system Settings → Battery.
Go to High background power consumption.
Find your app in the list and enable the high battery consumption.