Here is a step by step instruction on how to do it!
First, make sure that your current view in the Settings > General > Audience Visibility includes Subscribed users only:
Then go to your Audience tab, choose all of your current subscribers and assign a specific Tag to all of them using the Bulk Actions button, for example, 'subscribed':
After that, get back to Settings > General > Audience Visibility and uncheck the box to include Unsubscribed users into your current view:
Go back to the Audience tab and filter only those users who don't have the Tag you've assigned on step 2:
These are all of the unsubscribed users of your bot!