(C:) drive --> Program Files (x86) --> Steam --> steamapps --> common --> Nazi Bunker --> Files --> gamesaves --> Delete everything in the folder

Alternatively open steam, go to Library, right click Nazi Bunker, click properties, go to local files, then click browse. Open files folder, open gamesaves folder and delete everything inside.

When you save to a slot that has data saved to it already you have to click an extra prompt wasting time. Delete the data before each run and only save to empty slots.