How do I bill this?

We have a patient who had a previous EMG done in her PCPs office in April. The EMG was suboptimal and she needs another one. Can we do another one? How would we bill that so Medicare will pay it? Should we send supporting documentation with the billing? Also, where would I find out to make sure someone is a Medicare provider? We are trying to send Medicare patients to the providers in Medicare network. Thanks.

Found the provider site

I found the site that shows all the providers.