Adding implicts to unique items

How to add an implicit to a unique item other vaal or hertification?

Unique items can have corrupted implicits, and that's it. If it doesn't come with one then it's not getting one.

You can get enchants in a few ways, but these are not implicits.

Do you have a specific item that you're asking about?

Thank you for answering my question. I am however looking for the name of catalyst the gives higher quality for uniques boots, rings, amulet, helmet.

I believe you are mixing armour/weapon quality with jewellery quality:

Armour quality, as in Quality added to helmet, body armour, boots, gloves and shields, increases local defences for that item. For example, a Helmet with 100 ES and 20% Quality will raise to 100*1.2 = 120 ES. So far the only exception for this rule is Body Armour quality, which can be enchanted (this is not an Implicit) via Horticraft in order to provide different bonus than defences (for example, "add 1 life for 2% quality"). Armour quality is provided by Armourer's Scrap

Weapon quality, as in Quality added to any weapon, increses local physical damage for that item. For example, a One-Handed Mace with 10-20 PhysDamage and 20% Quality will raise to (10*1.2)-(20*1.2) = 12-24 Physical Damage. There are Horticraft enchantments (this is not an Implicit) which changes this bonus with another (for example, +1% elemental damage for 2% Quality). Weapon quality is provided by Blacksmith's Whetstone

Catalysts are currencies introduced by Metamorph League, they are not considered basic currencies like Armourers and Blacksmiths. You can use Catalysts on ring, belts and amulets in order to increase their modifiers if they have a specific tag.
Here is a list of all Catalysts

For the "Implicit is not Enchantment", PurpleChakra is on spot

Thank you