Hi,
I recently did this myself. First of all, you need an NHS number. Then you need to go to NHS.co.uk and then click on "Find and Choose Services", then "GPs" and then you need ti type in your postcode and a list of the nearest surgeries will come up. Then you need to ring one of them up and see if they have space. Some might be full but if you ring other ones in the area you will get one which has space and you can register with them.

Good luck - get well soon!