Click the blue "Select File" button on the left-hand side.
Open your File Explorer (or press WIN+R).
Use the navigation bar to enter the following path:
%appdata%\..\LocalLow\Pugstorm\Core Keeper\Steam\
steam_id
Foldermaps
FolderSelect the maps
folder
Choose the folder with your character id. This should be in the same order as in-game.
Select the map file. There is no easy way to figure out which map is the correct one. It also includes maps of servers you visited.