Howdy Qbc-Apple-user,
I understand you're looking for assistance with updating your vaccination record to be shown via the Wallet and Health app, so check out the following information to see if this helps.
With the QR code that you were provided, are you certain that it is compatible with the Wallet and Health app? If you're uncertain, confirm this so you're certain that this should work.
Once you've confirmed this should work, let's be certain that the latest iOS version is installed. If you see that an update is available, be sure you have a recent backup of information. If you need assistance with either of these steps, check out the following resources:
How to back up your iPhone, iPad, and iPod touch
Update your iPhone, iPad, or iPod touch
After confirming you're up to date with the latest software, give this a try again. As a refresher, work through the following resource to confirm the steps are the same as what you're taking:
Add verifiable COVID-19 vaccination information to Apple Wallet and Health
If you're still needing assistance after working through those steps, Contact Apple Support to look into this in more detail.
Have a great day!