If you have the User's Guide, the setting for Live View is on page 74. If you don't have the User's Guide, you can download it from the Olympus site. To get to the setting, MENU > gear > D. Scroll down to Live View and turn ON.
Since you are using a Nauticam housing, and the FO ends press in with rubber plugs, you might try using a Q-tip and making sure the FO ports on the housing are clean. You may have a bit of goop in there that is obstructing the light path when wet.