Hello! 
Soulmask has an offline single-player game mode. This is what people are using the trainer for.
Just don’t select the online game option when setting your game up. An offline game session is running on your own PC rather than a server.
Many games have the same feature - to play solo by default or have the option to take the session online, such as The Lord of The Rings Return to Moria and Conan Exiles (SoulMask is pretty much a copy/paste of Conan Exiles, with better graphics). Of course, using a trainer, you should play solo.