What should I do if the tyre is rubbing against the mudguard?

That's easy to fix by readjusting the mudguard. All you need to do is loosen the left and right bolts in the stay clamp (near the wheel axle) and adjust the left and right stays so there is at least 6 mm between the tyre and the mudguard. Once you are happy with its alignment, re-tighten the two bolts in the stay clamp.