Mega Speedup is given to a Mega Stone equipped Pokémon on the Support Pokémon selection screen to permanently give that Pokémon a slight decrease in the number of matches it takes for that Pokémon to Mega Evolve.
To use the Mega Speedup:
Navigate to the Support Pokémon selection screen (from the main screen, tap the Poké Ball icon on the lower right.)
Select the Mega Speedup icon (this looks like a rainbow-colored candy) and drag it onto one of your Support Pokémon who can Mega Evolve.
Note: for your Pokémon to Mega Evolve, you must have captured that Pokémon and have obtained that Pokémon's Mega Stone.
The game will ask you to confirm that you want to use up the Mega Speedup on this Pokémon.
Can’t find what you’re looking for? Click here to submit a service request form.