2 things i need help with

1- I no it isnt just plain luck that a pkmn joins ur teem, but i dont no how 2 do it on purpose?(p.s. i hav articuno)

2- I lost the HM dive and i cant get into the stormy seas and it has the little "go" symbol next 2 it so i cant get there, how do i get it back?

1. There's no way to do it on purpose!!! But if you put on a friend ribbon, it boost your chance of having pokémon joining you by 10%. Also, the pokémon only join you if the team leader has done the final blow, it's adjacent to you and you have the pokémon's friend area.

2.You can get Dive in Solar cave 10F but don't forget to bring a key for opening the lock and a flying(that float!) or a water pokémon because it's surrouded by water. In the same cave, you can also find Surf(20F) and Waterfall(15F).