Been having an issue with creating a magic weapon, that grants a bonus to the one handed skill when used.

I creating an effect with the following properties:

Effect: Peak Value Modifier

Casting Type: Constant

Delivery: Self

Assoc Item 1: One handed Power Mod

made sure to select no duration.

Then turned it into an enchantment, and set the magnitude.

But I can't select the enchantment when adding an enchantment to the item in question.

Once you've made a Magic Effect (the base effect) you often also need to make a spell/potion/enchantment that references that effect.

I'd suggest looking through how some vanilla Enchantments and Magic Effects are configured. Good luck