You must register your bike on the Focus website. You should have been told the exact web address on the paperwork that came with the bike. But you should be able to find it easily enough by going straight to the main Focus home page. Once registered, if/when you need to make a warranty claim, they know who you are and that the bike is registered to you and they know who sold it to you. In addition, I make a note of all the various numbers on the frame, fork, shock for future reference.
For example, frame numbers:
Bike serial number: 386###-### P/N: 6335##### ISO4210-2/EN15194 (top of down tube)
Frame ID: A118G##### PD1-1-###-# (bottom of seat tube, rear facing)
Rear Triangle ID: A118H202##### PD####-9(29) (inside non-drive chain stay)
I have blanked out some digits.
I don't know whether all bike shops do this, but if Rutland Cycles sell a bike, they will pursue warranty claims for the owner even if the owner did not buy the bike from them. They make a standard charge of £35 for this service, just about everything else is free. I say "just about", let me explain. If it's a motor or a battery or a frame then yes it's free. But if it is something that there may be arguments about like "how did the electrical cable get damaged?", then they have discovered that the chasing about to establish this is not worth the effort, so you pay for the cable and are free to pursue whoever you think is liable. I had to do this and JEJames paid up without much bother at all.