its pretty simple, equip a insured loadout before deploying, then run to an exfil site call for an exfil kill all the zombies there and once the helicopter comes dont go on it wait for the helicopter go away and re call it and do the process again
so that method has been patched honestly best way to kill zombies quickly is to do contracts like spores secure areas and such and just dont finish the objective zombies will keep on spawning and you just kill them