Unable to open database after losing data file
You just need to restore or catalog the backups which were stored another location. Follow the following steps. 

I assume that you have spfile, controlfile and redo log files in place. 

As you said you have copied the RMAN backup in another location, restore that backup to your regular backup location. 

Catalog the backup files.

RMAN&gt; catalog start with '/u01/app/oracle/fast_recovery_area/backupset/';


Then use RMAN to restore database. 

RMAN&gt; restore database;


Recover the database with available archived logs.

RMAN&gt; recover database;


Then simply try to open the database(use resetlogs clause if you performed incomplete recovery).

SQL&gt; alter database open;


OR

 SQL&gt; alter database open resetlogs;


Done!