Since this is an older custom ROM, official download links might be hard to find directly. It is typically found on: XDA Developers Forums (POCO X3 Section) Telegram Channels (Poco X3 NFC Updates)

Boot your phone into Recovery Mode (Power + Volume Up). Wipe: Wipe Cache, Dalvik, System, and Data. Optional: Format Data (if coming from a different ROM).

You may need to flash the corresponding vendor/firmware separately if instructed. If you'd like, I can help you find:

Select Install , choose the miuipro_v11_surya.zip file, and flash.