2 answers
To create a new Agentforce/Data Cloud Org, you need to delete the current one, and only after that will you be able to create a new one.
To delete/disconnect Agentforce/Data Cloud Playground, you need to follow these steps:
1. Open the list of your Playgrounds (SF Orgs) at https://trailhead.salesforce.com/users/profiles/orgs.
2. Create a new "standard" Playground.
3. Once the Playground is created, you will be able to delete/disconnect the Agentforce/Data Cloud Playground.
Now you can create a new Agentforce/Data Cloud Org.
Sincerely,
Mykhailo Vdovychenko
Bringing Cloud Excellence with IBVCLOUD OÜ