Reverting a failed primary into the new (original) primary db again

Hi,

We recently did a fail-over to a standby database due to hardware failure on the original primary DB server. The original primary DB server is now fixed and we want to make the database on it as the primary db (like on the original configuration). What would be the best solution we could do considering the following:\

1. Flashback DB is not enabled on original primary

2. No backup on original primary, the only backup we were able to take was backup on the NEW primary after the fail over.

Thanks!