Default tipping is not set up on new accounts. In order to get to the tipping and set as default, go to settings -> Payment Preferences -> Tips -> Preset Tip Percentages. This is where you can choose a default tip for your customers during the checkout process. You can also customize a different tip amount, too.
In this example, the customer will be tipping 10% by default. If you have "Show Custom Tip Option" selected, your customer will be able to choose their own tip.
During checkout, this is what the customer will be able to see:
Here is some more information about tips.