I assume you migrated from JIRA 6.x to JIRA Software recently? The Agile menu item has been removed and has become an integrated part of the JIRA Software product.
Everything you need is in the documentation over here.
When the docs mention 'navigate to the backlog of your desired board', the board must be a scrum board. Use the button in the left sidebar highligted in the below screenshot:
I’m a designer on the Jira team. For a long time, I’ve fielded questions from other designers about how they should be using Jira Software with their design team. I’ve also heard feedback from other ...
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