You have a few options. Which options are open to you depends on which specialty you are applying for now, which specialty you want to switch into, and how competitive of an applicant you are.
- You could apply for your new specialty right now. This also depends on how quickly you can pull together a second app, including a second PS. If, for instance, you want to switch into derm, but can't get a single derm LOR, you're screwed.
- You could take a year to do research, or apply for a non-designated prelim medicine or surgery year.
- You could keep your current app as it is, purposely not go to a single interview, submit a bogus rank list, with the intention of not matching. Then, you could scramble into an open spot in your new specialty of choice. This depends on how competitive your new specialty is. It could work for FP, not so much for ortho. Also, you have to submit a fake rank list; otherwise you do not gain access to the list of scramble spots.
- Finally, I would talk to a PD of the field that you are trying to switch into. He/she might offer some insight.