You will need Cheat Engine to load the cheat table that will activate the invert mouse function.

Step
1. Run the game.
2. Attach the Cheat Engine to the game process.
3. Download cheat table from this link[drive.google.com].
4. Open the downloaded file in Cheat Engine.
5. Click on the checkbox in front of "Invert Mouse" item on the cheat list to activate invert mouse look.

Bonus
The game speed option can be changed to increases or decreases the game speed. (Default is 60)