Basically you contact them via contact form: https://mysupport.razer.com/app/warranty-support/ (or live chat option if available for your country).

Yeah, its better to just avoid Razer in the future.
My left mouse button is faulty after 3 months of light everyday use.. I can’t get warranty, because i don’t have the invoice…
I don’t have the invoice, because the link they sent redirected me nowhere to began with, and now its expired (without indicating anywhere that it will ever expire).
My old noname wireless mouse lasted 7 years of really really excessive use (it even got epoxy resin on it lol), and i only changed because its battery was giving up… It was a mistake…
Its expensive, the programs they have are often really buggy, and for some reason there are 30+ razer process running all the time, and even the hardware is bad, in 3 months i had issue with duble clicking, which just magically stopped at some point, i had connectivity issues, which again, just magically stopped at some point, and now the left click is releasing while button is still fully pressed.

Not to mention to constant issues of the hypershift button is default on when you connect the mouse, and you have to keep pressing it over and over again till it realizes that it isn’t pressed all the time. The fact that it just drops the connection pretty often makes it more annoying than it would be…

A simple mouse shouldn’t raise my blood pressure, but this one does…
I wish no one this misery.