You can done by this way
From your Shopify admin, go to Settings > Checkout.
In the Tipping section, check Show tipping options at checkout.
If you want to hide the tipping options, uncheck Show tip options to all customers. In this case, the customer must check a check box to display the tip options.
Under TIP OPTIONS, enter a value in percent in the Option fields. You can add up to three different values.