How to configure new created ItemType

Hello, I've just encountered a configuration problem. I hope that you can give me some advice. After I created a new ItemType by myself in a TOC category (for example: Manufacturing Process Plan), I was able to create a new instance of this type. However, since the "Operation" type of Manufacturing Process Plan can insert other types like "tools", "skills", etc, how should I do configurations so that "Operation" can also insert my created new ItemType instance? By the way, in the relation tab, I've also set up the relation to the "Operation". Thanks for your reply in advance.