You certainly can!
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Once you've created your primary profile in FitXR, you'll be able to create up to 4 more additional profiles.

To create an additional profile, when you enter FitXR you'll just need to select 'Create Profile' and follow the on-screen instructions.
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Once you've created this, you'll be able to choose which one you'd like to use from this first screen, and also switch between them from the profile section of the home menu. You can read more about this here.