Your Suunto Ocean has three buttons that have different functionalities when short pressing or long pressing them during the exercise.
In Freediving mode, the buttons have the following functions:
Upper button long press: Adjust brightness level (Low/Medium/High)
Upper button short press: Access the freedive options menu to stop exercise, use flashlight or discard exercise.
The menu is not accessible underwater.
Middle button short press: Change view (above surface only)
Lower button short press: Change switch window item
Lower button long press: Lock and unlock buttons