You cannot level up a Max Move directly in Pokémon GO
Max Moves are tied to Dynamax or Gigantamax Pokémon
To make a Max Move stronger, power up the Pokémon itself
Use Candy and Stardust to increase the Pokémon’s level
Unlock or improve the Pokémon’s Max Moves if the game offers that option for that species
Check the Pokémon’s Max Move page in the Power Up or move interface
Some Max Move upgrades may require specific resources or research progress
Evolve the Pokémon if its evolved form has stronger Max Move potential
Catch or obtain a higher-level Dynamax or Gigantamax Pokémon for better base strength