Individual Senators may unilaterally remove themselves from a Civil War within one turn of the Declaration of War that brought them into it by breaking all Oaths of Loyalty that tie them to any Senator involved in the War and by publicly declaring Neutrality. Neutrality cannot be claimed by a declarer, a target, or any Senator who has been involved in a PvP Battle during that specific Civil War.
You'll have to break your oath to Apionnas Vringas and then make a public IC post saying you are neutral.