If you would like to increase your chip count during a tournament, you can do so during the add-on periods.
When the add-on period begins, an 'add-on' button will appear. Click on the button and confirm your request before the add-on period ends.
If you run out of chips during an add-on period, you will automatically be offered the option to add-on. You then have 60 seconds to accept the offer or not.
Upon accepting to add-on, you will then receive two messages, one to inform you that the request is being processed and the other to confirm that the request was approved.
The add-on amount is transferred from your 'Available Money' to your 'Money on the Tables'.