In MTTs each player gets a designated extra time bank at the start of the tournament.
In order to use this it must be enabled or toggled on during play by tapping on the stopwatch icon.
Once activated this will automatically be in effect if you happen to go through your standard time bank when the action hits you.
Please note that the additional time allotted to you will not replenish during the next hand.
If you start a tournament that has given you an additional 10 second timebank and use 2 seconds during one hand you'll start the next hand with 8 seconds remaining.
You can toggle the additional timebank to be enabled automatically at the start of every tournament through the Settings panel found on the left-hand side of the screen.
By navigating to the "Other" section you will see a toggle to have this enabled at the start of every tournament automatically.