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 Folder
Select the folder with your steam id. If you see more than one folder, please check online on how to find your steam id.
maps Folder
Select 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.