Here is a Vivo X6A Stock ROM Firmware which can be used to load and flash stock firmware on any Vivo X6A of this exact variant. Any MTK Flash tools can download and flash this Vivo X6A flash file on your X6A so long as that MTK Flash Tool supports MTK Scatter File.
Since most major software malfunctions on any MTK Android devices can only be corrected by flashing, this X6A flash file, if properly used, can unbrick (debrick) your X6A and also corrects any software issues your Vivo X6A may currently have. Also, keep in mind that when you load stock firmware on your Vivo X6A using any MTK flash tool, your Vivo X6A will be reset to factory defaults settings and by that, definately, your UserData will be lost including contacts, messages and others.
Note: If your X6A is already bricked and you want to unbrick it, you will need to pay closer attention to the tutorials contained below here.
Vivo X6A Stock ROM Firmware Download Link(s)
How to Flash Stock Firmware On Vivo X6A
1. Download your Vivo X6A stock ROM firmware from the link above.
2. Extract the Vivo X6A Firmware you downloaded from the link above onto a folder on your PC.
3. Download and install MTK android device drivers on your PC. You may skip this step if you have installed MTK drivers on your PC already otherwise, download MTK drivers here
4. Now, choose either of the tools listed below here to load the stock firmware on your Vivo X6A.
2. NCK Box
3. Miracle Box
See video tutorial here: How to Flash MTK Android Devices Video Tutorial
Note
1. Each of the tools listed above contained step by step guides with illustrated pictures on how to flash stock firmware on your Vivo X6A.
2. If your device is bricked already, I recommend that you use NCK Box or SP Flash. Both are the safest toolS for flashing MTK Android devices.
3. If you require any further assistance, simply drop your comment detailing the issue(s) and I shall help you revive your Vivo X6A, if need be.