You have to have helped all the Kimona girls. Then you go to the dance theatre in Ecruteak and you battle one and then the next 4.
Defeat the kimono girls
the kimono girls are in ecruteak city in the dance theater
You first have to beat team rocket, then the Kimono girls
Back where the kimono girls were first in there dancing place in erecutek city
Eruteak dance theater
In heartgold you need to have all 8 badges and have defeated all 5 of the kimono girls and then go up the tower. At the top will be the kimono girls and they will do a dance that summons ho-oh.
Assist the kimono girls at the dance hall and an old man will give you it.
Here are their pokemon-their weaknesses:Umbreon-Espeon-Flareon- Any water-type pokemonVaporeon- Any electric-type pokemonJolteon- Ground type pokemon, I recomend Geodude's evolutions(Graveler, Golem)
After defeating the 5 Ecruteak's Kimono Girls they'll give you the Clear Bell.
You need to defeat the 5 Kimono girls in Ecruteak city and talk to the father.
They are in Ecruteak City in the Dance Theatre
You need to defeat Clair the Blackthorn City Gym Leader and then defeat the 5 Kimono Girls and then you'll be given a bell and you'll be able to take it up to the top of the Tin Tower in order to summon Ho-Oh in Pokémon HeartGold.