Life is simpler if one Arduino is always Master. And the other is always a Slave.
The Master "speaks" to the Slave whenever the she wants. The Slave does as he is told.
The Master can periodically ask the Slave if the Slave wants to talk to her.
The OLED is always going to be a Slave. The Master is in control of the OLED.
Yes, it is possible for the Slave to "become" a Master in a "Multi-Master" environment. But this is more trouble than it is worth.
Think about the real world. Life is "smoother" if you avoid fights and just do as you are told.
David.