How to evolve Meltan in Pokemon GO is important information, as you can only evolve this Pokemon in Pokemon GO. If you want to get Melmetal in other games with Pokemon Home, you will have to go through GO first to get it.
How to Evolve Meltan in Pokemon Go
Meltan evolves pretty simply. You just need 400 Meltan Candy, which is easier said than done. You have to get the Candies the usual ways: catching Meltan, sending it to Willow or just having it walk around as your buddy.
You also get Meltan Candy when you send Meltans to Let's Go Pikachu or Eevee.
According to a Pokemon Home leak, Melmetal will apparently have a Gigantamax form in Sword/Shield. It is currently unknown how to obtain this form, or if it has anything to do with Pokemon Go.