howto remap keys on steelseries apex 3

its the funktion key next too r-ctrl.

for 20 years i used that button to RELOAD my rifle in all fps-games

and have now steelseries apex 3 installed.

now nomore reload,byebye apex if i dont find fix the 48 hours

i vould loove too change that funktionkey too > that < on left side at Z

but cant find any software there can doit .

anyone have a idea about my problem,there could help me