To load each of the checkpoints in the folder

follow these steps:

[1] Press "Win + R" and type "appdata".

[2] In this folder, go to "Local", then to your game's folder ("The5thFloor"), then to "Saved" and "SaveGames".

[3] Finally, in the downloaded checkpoints folder, find the checkpoint you want. You'll recognize them as "DarkPals_Backup" and "DarkPals_Game". Copy them (Ctrl + C) and paste them, replacing the existing files (Ctrl + V) in "SaveGames" within the game's folder from step [2].