It’s always nice to have options. Once you have finished the story mode, you can replay any stage exactly the way you want. Chase that highscore, and compare yourself with other zombie slayers!
As a southpaw myself, key bindings are often annoying in games. Half the time you can’t rebind all of them, or some of them are hard coded (especially looking at a certain company starting with the letter “B” that’s famous for old people scrolling). Not in GROSS. All keybindings can be changed. Aaand you don’t get one, or two, but THREE bindings. Well, six actually. Three for keyboard & mouse, and three for your controller. If you’re a weirdo that plays a first person shooter with a controller. But we don’t judge. Weirdo.
Anyway, in case you’re ever lost because you forgot what key reloads your gun, the only key you really need to remember is the Help key (bound to H and R3 by default), and all your primary key bindings for your current input device are shown on screen for a couple seconds.