LIGHT is built so you do not start over. Log in with the PUBG MOBILE account you already use. The public line is that owned items and cosmetics come with you, and you can still squad with friends on the standard app.
What you should never do
Do not give your password to a “LIGHT linker” website. Do not buy a “ready LIGHT account.” Those scam patterns show up around every mobile launch.
If your main account is already banned, LIGHT is not a backdoor. Anti-cheat is still the operator’s.