I assume most people here already are registered but just in case: here’s the link.
https://www.gov.uk/electoral-register
What happens if you do not register
You must register to vote if you’re asked to do so and you meet the conditions for registering, for example you’re 16 or over and you’re British or a national of an EU or Commonwealth country.
If you’re asked to register and do not, you could be fined.
You shouldnt confidently state things that you are uninformed about