Using RSEdecode Youtube Tutorial Link
RSEdecode is to check the IV and the PID of the pokemon, which is important.
1) Put the desired PKM to check for its IV in the 2nd Slot
2) Create a folder in C drive and call it rsedecode
3) Click Tool --> Memory Viewer, Click 32 Bit and Click Go on top right
4) Click save, you will see a pop-up
5) For Address, it is different depending on the game:
Emerald - 2024550
Ruby/Sapphire - 30043C4 Fire Red/Leaf Green - 20242E8
Size: 64, then click Save in rsedecode
6) Save as monster.dmp in C:/rsedecode
7) Press Start --> Run --> CMD, type cd \rsedecode, follow by typing "rse".
This will give you the IV of the pokemon, now plug the data into PokeRNG