Anki isn't really a flashcard app, it's a sophisticated system for spaced repetition (read more
here for a more detailed explanation of that concept). We don't have the option "reverse the deck" because there's no such thing as "reversing a deck" in Anki (instead we have "note types"). If you try to rush into the advanced features of Anki without first understanding things like what is the difference between a note and a card, what is a template, etc, you are likely to be frustrated. I strongly suggest reading through "
the basics" section of the main Anki manual in its entirety. After understanding the background information, it should be obvious to you how to accomplish what you want.
I strongly suggest keeping the reverse cards in the same deck as the forward cards for now... It's possible to separate them, but you'll need to make a dedicated template and use the deck override feature, which might involve going a bit deeper than you're willing to go.
To change all of your cards to a note type with a reverse card, you will need to use Anki Desktop, as it's not currently possible to do bulk operations with AnkiDroid. Use the cloud sync feature to get your cards into Anki Desktop. Then in Anki Desktop:
Open the browser, choose your deck, press "ctrl+a" to select all cards, and then choose "change note type" from the edit menu and choose the "basic and reversed card" template.