How do I make a "When on head" or "When in hand" item? Like max health or speed but in that vanilla style way.

I know something like this is possible with commands, but how might I do this in MCreator? I'd like to make items that give boosts without potions, so they can stack properly. Like if I have a helmet that gives +5 health and a chestplate that also gives +5 health, if I do it via potions, wearing both would be the same as one, but it's supposed to give +10.. How do I make the NBT or whatever item data that does this?