Welcome to Subeta! Your HA actually looks pretty content to me, so I'm not sure if you've fixed the problem or you want to appear even more gleeful, but yes you can change your mouth :)

There are some wearables that give you lips/a certain mouth, if you want to use those you can drag the base 'mouth' layer below the 'base' layer, so that you don't have two mouths on your face.

Alternatively (and more easily), under Personal > Wardrobe > Base there's an option to change your mouth style :) Make sure you press 'Wear' after you have selected one you like to apply it to your worn avatar.

Let us know if you are having any problems!

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