Tap “Strategy” in the main menu on the bottom of the screen.
Tap the “Edit Goal” button. You can find it in the row of buttons directly below the “Strategy” header, and also a bit further down the screen in the widget summarizing your current goal.
Adjust your target rate of weight gain or weight loss using the slider.
Make sure to tap the checkmark at the top of the page when you’re done to save.
Note that editing a goal is just for changing your target rate of weight change. If you’d like to set a new goal weight, you’ll need to create a new goal.