How do I change my default playground in Trailhead to my developer playground? I'm unable to disconnect the other playground that I don't need.

@Courtney Williams I was not aware that Salesforce employees could not create a specific dev edition. It is the first time I read that. Sorry to ask but are you sure you did not fill in the username inputfield with your Salesforce corporate email (that should be linked to your Salesforce instance username) ? In this case, have you tried using a personal email & well filled in a customized unique username to test ? Eric