Hold the button while connecting it to the PC via USB. The LED should turn green (Flashmode).
: The most reliable way to find specific regional firmware is via the XperiFirm tool , which allows you to select the " Download 502SO 340 R13C Remove Lock ftf
If you prefer not to use third-party flash tools, you can use official software: Xperia X Performance driver | Developer World Hold the button while connecting it to the PC via USB