How can I make the amount of damage an item does change?

does the item have damge when you use it

Try using the "before entity hurt" event instead, using the same method I mentioned before.

Then what generator ARE you using? Keep in mind that many generators are going to be missing a lot of support in relation to the main ones natively supported.

Alright, well...you have two options. Use the attribute modifier blocks to add to the default base damage for whatever item the entity is holding (these here: https://gyazo.com/358719d2abebc034bff2a5fa9c3a6298, and keep in mind when you set one, it disables all the other defaults (like attack speed), so you have to add that in as well), or you can use my plugin here: https://mcreator.net/plugin/65847/dtms-toolkit, allowing you to set the attack damage for the provided entity. So you can use that to set the damage of the entity (to deal extra damage) depending on a specific condition, then set the damage back to default when that condition is over.