Shadow Pokémon in Pokémon Go have their benefits and disadvantages. While they typically have stronger stats, they also come with the charged move Frustration. The Pokémon cannot unlearn this charge move unless there are special conditions met during a special event. These events are extremely rare.
On December 10, 2020, players will be able to do this during The Game Awards. While the Awards show occurs from 7 PM to 11 PM ET, the Pokémon Go Event kicks off at the same time but continues into the next day, so it’ll be from December 10, 7 PM to the 11 at 7 PM ET. You do not need to watch The Game Awards show to participate in the event or input something happening.
The event also increases a trainer’s incense strength, how much Stardust they receive from capturing Pokémon, and Team Rocket grunts will be appearing more often at PokéStops and balloons. It’s a good way to ensure all trainers give their ideal Shadow Pokémon an empty slot in anticipation of the December Community Day 2020 event. During that event, all Community Day Pokémon from 2019 and 2020 will be appearing on Saturday and Sunday, which means any trainers who needed to teach a Pokémon an exclusive charge move or missed out on can participate.
Make sure you’re in-game when the event happens. When you have a Shadow Pokémon with Frustration, all you have to do is give them a Charged TM starting on December 10 at 7 PM ET, and you have until December 11 7 PM, and they will forget Frustration.