Simply start the "Activator.exe" and then start Dead Island Riptide. If all goes well the Activator will close itself... 

Now when you're ingame press the [ESC] Key to  show the menu. On the bottom you'll see the developer menu...

• Dead Island: Save Game (Start The Game, Sam-B, full upgrade) [2019-Sep-03]
• Dead Island GOTY: Table for Cheat Engine +11 Steam v1.3.0 {VampTY} [2019-Apr-11]