Good news, publishing to Apple Podcasts Subscriptions through Acast is automatic, once you have set up your accounts and you have told Acast which tier should be connected.
When you publish a bonus episode to the tier associated with Apple Podcasts, Acast will also deliver that episode to your Apple Podcasts Subscription audience, no additional effort needed.
Here is an example of setting up a podcast with Apple Podcasts subscriptions and Acast+, and the publishing of a bonus episode.
Here is a video showing you how to set up to publish to Apple Subscriptions:
Here is a video on publishing. Episodes will remain in draft until Apple has finished processing: