You can't. Unless you do new things for the first time, such as go to Friendship room, etc.
"Muhaha! Hmmm... I feel it! The twinkle in your eyes! The twinkle of friendship! You're quite something. Your Pokémon is quite a Pokémon! It's ready to participate in the Pokéathlon, bud! Most of all, your solidarity with and trust of Pokémon makes me Believe in infinite potential! All right. Follow me! What do you think? This is the Pokéathlon Dome! Pokéathlon is a Sports festival for Trainers and Pokémon! Inside the Dome are various challenges awaiting Trainers and Pokémon to test their friendship. Why don't you try it? You're amazing, bud! This is a pleasant surprise! To see a Pokéathlete with strong potential Is such a pleasure! I'm glad I held the Pokéathlon here in Johto. ...My name is Magnus. We shall meet again, bud. See you, young Pokéathlete!"
"Oh gosh! You are...! It is indeed you, ! Outstanding! Quite an achievement for you to come up here, bud!"
"This is the "Friendship" room. It was built to commemorate the solidarity, trust, and potential of Pokémon and people and hope for the eternal friendship between Pokémon and people."
"Congratulations! This room is only for those true Pokéatheletes who have earned real friendships with Pokémon! ! You are a true Pokéathelete, bud! Having said that... This is also the moment of a new beginning... That's right, bud! You have just heard a new starting signal. Your challenge continues for a whole new height and to become the legendary Pokéathelete! Take a look at this statue. You may be looking at your goal..."
"This is the "Friendship" room. It is the last of all. It's the room where eternal friendship between people and Pokémon is pledged ...But this is not your goal, bud. Each room has Trophies to earn, but you can aim for any new height. It is entirely up to you whether you get there or not... That's right! Your true goal is not something anyone else can decide for you, bud. ! You can overcome any difficulties with your friendship with your Pokémon."