I've checked that you opened a ticket with our support related to the same question.
Currently, it's possible only to add Stories into Epics via the backlog of your board.
We have feature request suggesting the implementation of such ability:
Hi Community! The submissions are in (and listed below) for the 🍻🍂Apptoberfest🍂🍻 Demo Competition and it’s time for you to place your votes for the best: Analytics & reporting app demo ...
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