Follow this link and follow the instructions:

https://www.reddit.com/r/killingfloor/comments/3s9utd/killing_floor_1_bounty_20_trader_timer_skip_xpost

To access the Killing Floor files I followed this PC pathway: Start/Computer/OS(C:)/Program Files(x86)/Steam/SteamApps/Common/KillingFloor/System

And in there is where you want to unzip the Mutator Mod.

Once you've done that, boot up the game and go to Solo, hit Mutators; and there should be a new one to select at the bottom called "Skip Trader Mut" - add that to your active Mutators, and when you go into a solo game - at the end of the wave, hit your console button, mine is ` (the button next to 1) and type SkipTrader.

Badda-bing-badda-boom, you're on the next wave.

Good luck!