In order to set up or edit your Goal in Lark, tap on the Settings tab at the bottom of the screen.
Then, tap the "Customize my coach" section under General.
"Customize my coach" is where you can edit your Goal, Meal logging, and Diet Preferences. Your conversations with Lark could go into trends, suggestions/tips, and logging behavior.
By choosing a Diet Preference, you are telling Lark to avoid talking about certain foods. For example, if you choose "Vegetarian", Lark will not talk about meat. You can choose more than one Diet Preference from the list. Over time these settings will become more important as Lark gets smarter about what you're eating.
You can always manually log meals (as well as activities and sleep) from the Activity tab. Just tap the "+" in the top left of the screen to add something.