If you notice any software malfunctions with your Vivo Y51 android device, you're most likely required to download and flash stock ROM firmware on your Y51 to permanently correct the software errors you noticed on your Vivo Y51. And when you load stock firmware on your Vivo Y51 using any Qualcomm flash tool, your Vivo Y51 will be reset to factory defaults settings and by that, definately, your UserData will be lost including contacts, messages and others.
If your device has been bricked and want to unbrick it, you will need to pay closer attention to the tutorials contained below here.
Vivo Y51 Stock ROM Firmware Download Link(s)
2. Vivo Y51_PD1510F_EX_A_1.16.2_LA.BR.1.2.1_01210
How to Flash Stock Firmware On Vivo Y51
1. Download your Vivo Y51 stock ROM firmware from the link above.
2. Extract the Vivo Y51 Firmware you downloaded from the link above onto a folder on your PC.
3. Download and install Qualcomm android device drivers on your PC. You may skip this step if you have installed Qualcomm drivers on your PC already otherwise, download Qualcomm drivers here
4. Now, choose either of the tools listed below here to load the stock firmware on your Vivo Y51.
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 Y51.
2. If your device is bricked already, I recommend that you use Tool Studio eMMC Download Tool or QPST QFIL.
3. If you require any further assistance, simply drop your comment detailing the issue(s) and I shall help you revive your Vivo Y51, if need be.