Ability Patch
From Pixelmon Wiki
The Ability Patch is a type of medicine that changes a Pokémon's Ability from one of its standard Abilities to its Hidden Ability. It cannot be used to change a Pokémon's Ability from its Hidden Ability to one of its standard Abilities.
It can be obtained as tier 3 special drop, as a possible drop from Ultimate Boss Pokemon and from 4-5 star Max Raid Battles.