Catch Kubfu during its available Pokémon GO event or Special Research
Earn enough Kubfu Candy
Choose the evolution path:
Evolve Kubfu into Single Strike Urshifu with 200 Kubfu Candy and 50 Dark-type Pokémon caught while Kubfu is your buddy
Evolve Kubfu into Rapid Strike Urshifu with 200 Kubfu Candy and 50 Water-type Pokémon caught while Kubfu is your buddy
Make Kubfu your buddy before completing the catch requirement
Tap Evolve on Kubfu once the requirements are met