When you first start Pokémon Scarlet and Violet, you will be given an appearance option for your character from a list of premade options. These are not the final selections, however, and are just starting suggestions. This is because you are also given control over some individual elements of the look as well, some of which are bold and others are more subtle. One of the last, more subtle customizations you can do is to choose a beautiful place (or two) for your character.
With a total of 14 different beauty spot settings (including no beauty spot,) your options for beauty spots are quite limited, especially compared to other choices like the wide range of contact options in the color you want. You also cannot choose a color for the beauty spots, only their location (from some preset locations) and in some cases the locations of two simultaneous beauty spots. With these limitations, it makes sense that these beauty spots are more of a final touch for your overall look, rather than being the focal point like your hair or clothes. Also note that some of these beauty spots are not visible in some hairstyles.
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As with most of the other appearance settings in Pokémon Scarlet and Violet, you can change your beauty spot selection at any time in the Looks menu (left on the D-pad, followed by +.) Additionally, as with all other game appearance settings, none of these beauty spot options are gender locked.