If there was one person assigned as a workspace admin for the training environment, what happens when that person leaves? How do people get access?
Easiest way is to ask another workspace administrator that has access to that workspace. There are usually more than one - these are the model builders.
If there aren't any, you can ask the tenant administrator (this is someone that has access over the entire tenant)
If you know your Anaplan business partner you can reach out for help.
Lastly, you can log a ticket with firstname.lastname@example.org.
Some people from Anaplan always have the access to your workspaces.
They are your business partner and some other key folks from Professional services or from Dev team.
Best would be reach out to your Business Partner or ask your tenant admin to write to Anaplan support folks (email@example.com).