If you already have the custom state set up, it is the same as setting a dynamic expression you have already done in your workflow for creating the event, just set up the dynamic expression to point to the custom state value.
If you are interested in 1:1 lessons to help get you past significant road blocks, feel free to reach out to my in private message, as it is a service I provide.
I’m very well versed in scheduling as I’ve created a very complex scheduling application being sold as a template