Changing firmware in the phone will erase all of your data.
All described operations you are doing at your own risk.
If want to save your data do a backup before starting.
A battery must be at least 60% if not you will kill the phone completely.
1. First of all, we need to find out the exact phone model that we've got.
also, you can find it in Xperia X Performance phone menu as shown below
7. Download firmware by pressing firmware version button.
8. After the download is finished close XperiaFirm, now FlashTool will ask you if you want to add downloaded firmware to the database click the YES button to confirm.
9. Next press the lightning button,
10. Select Flashmode and confirm with OK button.
11. Select SONY Xperia X Performance phone model and model number of your phone, firmware customization and firmware version the one you've downloaded in step No. 7.
14. Connect turned off Xperia X Performance phone to USB cable with pressed volume down button.
15. Release volume down button when you see "Device connected in flash mode" information in FlashTool windows log.The flash process starts, now just wait until process end.
16. After all disconnect Xperia X Performance phone from the USB cable. Turn it on with the power button and leave it on a flat surface until the phone turns on completely
(this is very important otherwise the phone will not complete the first start and you will see an error message on the phone screen).
17. Congratulations your flash process ended successfully. Now you can enjoy your SONY Xperia X Performance with new firmware.
02 Feb 2022