there's not much info on your phone. i always look at xda.com as my main source for rooting phones. i also look to see if there is any developers support for any phone. for me no dev support=no fun. no dev support also equals no custom recovery or custom roms. this is the only reason i would ever want to root a phone.....especially having a custom recovery....that is key.
a custom recovery lets you make a complete backup of your phone called a nandroid backup....among other things recovery can do. i would not want to mess around deleting or flashing things unless i have a recovery.
and there really is not anything on xda save for this thread:
https://forum.xda-developers.com/general/rooting-roms/how-to-unlock-bootloader-vivo-phones-t3686690
but i do not know if it applies to your phone or not.....sorry but you might be sol on rooting your phone.....next time pick a better phone that has support for rooting.....like a pixel phone.