If you’re on a youth mobility visa you will be able to register for a GP online or in person.
Your youth mobility visa does not mean you will be unable to register with a GP. You will have paid an International Health Surcharge (IHS) which means you will access everything that the NHS has to offer.
You can register for a GP here:
How to register with a GP surgery – https://www.nhs.uk/nhs-services/gps/how-to-register-with-a-gp-surgery/