Compiling your Pokémon Go collection will certainly take a lot of time and patience. Collecting the right amount of Pokémon candy and other required items will require a lot of research and sometimes just normal walks. With the introduction of Helioptile during the Power Plant event, here's how you can evolve Helioptile into Heliolisk in Pokémon Go.
As with the evolution of Helioptile in the main games, you will need a Sun Stone to evolve one into Heliolisk, but in addition you will need 50 Helioptile Candy. As is the case with other Pokémon, you can collect three candies by capturing one Helioptile and another by transferring them. You can use Pinap Berries to give yourself a bonus amount of candy from the catch and if you set a Elioptile as your friend, they will find candy as you walk with them.
Unfortunately, there is no guaranteed way to get a Sunstone, but the best method is to walk around and spin Pokéstops. This way you only have a small chance of earning one of the evolution items, so don't expect anyone on the first try. Also, if you spin Pokéstops for seven days in a row, you'll have a high chance of getting an evolution item on your first spin that seventh day. Completing seven days of field research also gives you the opportunity to earn one.