Open PKSM on both 3DS systems
Make sure both systems have the same Pokémon game generation
Connect both systems to the same local wireless environment if required by your setup
Open the save file in PKSM on the source 3DS
Select the Pokémon you want to evolve by trade
Use PKSM’s trade or send feature to move the Pokémon to the other system’s save
Open the destination save file in PKSM on the other 3DS
Receive the Pokémon into the target save
Save the changes on both systems
Launch the game on the destination system
Check whether the Pokémon evolved after being traded
If it did not evolve, use PKSM’s edit function to manually set the evolved form
Save again after any manual changes