These tools are in Profile › Responsible gaming.
Per-tournament stake limit: it caps what you commit to a single tournament ($5, $10, $25, $50, $100 or an amount of your choice). Lowering it is instant; raising it goes through support, to allow time to think.
Taking a break: 1 month, 3 months, 6 months, 1 year or permanent. During a break: no deposits, no tournaments (even free ones), but your withdrawals stay open. A break applies immediately and can never be shortened, not even by support; you can only extend it.
If gaming becomes a source of stress, talk to someone close to you and don't hesitate to get help from a professional or a gambling support organisation in your country.