Many creators do the following:
Make a post on their wall and click the bell to notify subscribers (As shown by Carlton) AND also add their announcement at the end of the latest episode they make (Ideally, the new chapter to post).
Letting readers know when the next chapter will be up appears when you prepare your episode but instead of publishing it, you schedule it. I don't know about the App, but in Desktop it should normally appear once you have scheduled your episode to post on a future date.
For example, for this comic (which I drew and Bijou Paradise is publishing) episodes/pages have been submitted to Tapas like how you would do for a normal episode, the only thing is that we changed the release date for a future one.