Hello gisela181,
Thank you for posting in the Apple Support Communities and for reviewing the related article Use the Health app on your iPhone or iPod touch. From our understanding, you've been unable to sync the Vitality app to the Health app on your iPhone. We're here to help.
Are you the only person who has access to the Apple ID that's signed into all of your devices? In other words, do you share an Apple ID with a spouse or other family member? We ask because if the Apple ID is used by someone else, that could be why you're seeing the error "Health app linked to another user."
To help keep all personal data and apps separate - if an Apple ID is currently being shared - we suggest each person creating their own Apple ID, then using Family Sharing to share info like purchases. Check out the details below:
Make sure that each family member has a unique Apple ID
If this concern continues after taking the steps above, our resolution is to contact Apple Support directly. Depending on your region, you may be able to reach them here:
Get Support
We hope this information is useful. Kind regards.