http://www.swtor.com/info/news/blog/20160420
If you want to equip a Weapon Tuning the first thing you’ll need is a weapon with an available Tuning Slot. Weapons that have a Tuning Slot come from many different sources including the Cartel Market, PvP, Operations, Reputation Vendors, Flashpoints, Heroics Missions, and Crafting Recipes. Be sure to check if your Weapon has a Tuning Slot!
Next, you’ll need a Weapon Tuning. They are currently only found in Cartel Market Packs. The first Weapon Tuning, Lightning, is available in the Plunderer Pack which launches alongside Chapter XIII: Profit and Plunder.
Once you’ve got a weapon with an open Tuning Slot and a Weapon Tuning, combining the two is as simple as making any other modification to your weapon. First, CTRL+Right-click the item to open up the Field Modification window. You can also take it to an Item Modification Station. Then simply drag the Weapon Tuning into the open Tuning Slot and hit “Apply”. Your Weapon will automatically begin using the effect created by the Mod!
