you done a failover to the standby database. you cannot revert back to PROD database as production. In order to do so you need to take backup of DRCP database and create standby using it and then switchover the database and donot failover again.
Since you have performed a FAILOVER, this is a one way process. If you were trying to test the role transitions, then you could have gone with SWITCHOVER which is a 2 way process.
Now, you are having only 1 database which is behaving as primary database and you do not have the standby database. If flashback was enabled on your old primary database, then you can reinstate it to behave as standby database.
Since you are using DGMGRL, you can refer this http://gavinsoorma.com/2009/06/using-flashback-to-reinstate-a-standby-after-a-failover/
If using SQL, then you can refer http://shivanandarao.wordpress.com/2012/08/28/dataguard-failover/