It will all depend on where you trained and where you want to teach. England, Scotland, Wales and Northern Ireland each have very different processes for qualification. I managed to requalify In Wales. It Was a very difficult process there. If you want to on me feel free. A good place to look for information on tes.co.uk. It is a website aimed at teachers and has lots of information. Good Luck the process is not easy
The process is different in each of he four countries of the UK AND depends on the country where you trained.
Questions: Where did your friend train and where are they planning to move to? Does your friend already have the right to work in the UK? Is your friend a native English speaker (or do they speak English with a high degree of fluency)?