You can create unlimited extra slot items at add-slot-items section in config.yml.
add-slot-items:A:material:PAPERname:'&dExtra Enchantment Slot &7(+1)'lore: - '&fDrag this item into your item to use!' - '&fApply for all items but have only 50% success rate!'add-slots:1chance:50success-actions: - 'sound: block.note_block.harp;;1;;1' - 'message: bFB98[EnchantmentSlots] &aAdd {amount} extra enchantment slot to your item!'fail-actions: - 'sound: block.note_block.bass;;1;;1' - 'message: bFB98[EnchantmentSlots] &cYou are not very lucky, slot item has broken!'B:material:PAPERcustom-model-data:5name:'&dExtra Enchantment Slot &7(+5)'lore: - '&fDrag this item into your item to use!' - '&f100% success but only work for diamond sword.'add-slots:5success-actions: - 'sound: block.note_block.harp;;1;;1' - 'message: bFB98[EnchantmentSlots] &aAdd {amount} extra enchantment slot to your item!'fail-actions: - 'sound: block.note_block.bass;;1;;1' - 'message: bFB98[EnchantmentSlots] &cYou are not very lucky, slot item has broken!'apply-items: - 'diamond_sword'