[ASM & Hex] how to modify Type-enhancing items in pokemon emerald?

I'm making an Emerald rom hack where I want to put emphasis on held items and I want to improve items like silk scarf or black belt so it increases the power of moves by 30% percent instead of 10% (which I think it's how much of an increase they give)

Change the item's held effect parameter from 10 to 30 in an item editor