While playing the game, press [F3]. A ticked checkbox labeled "Disable Console" will appear at the top left. Press [F8] to get a pointer and uncheck the box to activate the console window. Press [Enter], then type one of the following codes to activate the corresponding cheat function. Note: If you restart the game, you must press one of the overlay keys first, such as [F3], before pressing the console key.
Google Subnautica Cheats
oxygen = inf. oxy
nosurvival = Disables the player’s food and water requirements
bobthebuilder = a) fastbuild b) unlockall c) nocost d) fastgrow e) fasthatch f) radiation