You have two choices. You can reapply for an FP PGY-1 position via ERAS to start July 1. That involves all the same process as last year -- ERAS application, interviews, ranking and matching. Finding the time to interview while being a resident can be very challenging. You will need a letter from your current PD.
Another option is to try to find a PGY1 spot now. You'd have to contact FP programs individually, to see if they have open spots. There is no centralized list that I know of. You will still need a letter from your PD, but you would not use ERAS (you would use a copy of last year's ERAS application). If an FP program had an open PGY1, you could start anytime but should give your current program at least 90 days of notice. Your contract may stipulate more or less, and you should check. You might recieve some credit in FP for your OB work. Honestly, the easiest way to do this is to transfer to your institution's FP program, if they have one.