Remove the four fixing screws from the front, remove vent, buy new ones, screw them in place.

Did this exact same thing yesterday.

Just got to know what diameter exhaust hose you have. The vent covers come in 100, 125 and 150mm diameters.

I'd recommend getting a cover that doesn't have those flaps (we replaced our flappy one which was missing 4 of the 5 flaps with a fixed louvre grill. We got from Placemakers, but Mitre10 and Bunnings will have them.

https://www.mitre10.co.nz/shop/manrose-fixed-louvre-grille-125mm-white/p/172222?gclid=Cj0KCQiAtJeNBhCVARIsANJUJ2ET-ou8FXus0CYEQvhl7ZXk8VcF51rQYa0_rRO6s-KWjp-ROq6SzAYaArF5EALw_wcB&gclsrc=aw.ds

Just make sure when you pull the broken ones off, if they have flexible ducting inside, that you pull a bit of that out with it (so you can attach it to the new one).