Your PS3 must be running either Custom Firmware (CFW) like Evilnat or PS3HEN. Stock, un-modded consoles cannot install unofficial or manually downloaded PKG files.
If you have a legitimate copy of the DLC or are restoring backups: tekken tag tournament 2 ps3 dlc pkg download
This guide provides everything you need to know about Tekken Tag Tournament 2 DLC PKG files, what content they unlock, and how to safely install them. What is a PS3 DLC PKG File? Your PS3 must be running either Custom Firmware
Disclaimer: This guide is intended for educational purposes, particularly for those looking to preserve or access content on their own legally owned backups. Ensure you adhere to all local regulations regarding game modifications. If you'd like to get the most out of your game, I can also: What is a PS3 DLC PKG File
Use the "Install Package Files" option on your PS3 XMB or the "Install Packages" menu in RPCS3.