Hello Bazunitec,
It sounds like you're having troubles re-adding a reservation to your Wallet app on iPhone. In order to add the reservation, you'll need to take these related steps: Add, use, and share boarding passes, tickets, and other passes in Apple Wallet - Apple Support
Add, use, and share boarding passes, tickets, and other passes in Apple Wallet
With the Wallet app, you can add and use boarding passes, movie tickets, coupons, rewards cards, and more. You can also share some passes and tickets.
How to add a boarding pass, ticket, or other pass to Apple Wallet on your iPhone
1. Open the app, email, notification, or other communication that contains your boarding pass, ticket, or other pass.
2. Tap Add to Apple Wallet.

3. Follow the instructions on the screen.
4. If necessary, tap Add in the upper right corner.
If you don't see an option to add your boarding pass, ticket, or other pass to the Wallet app, contact the merchant or company that issued it to make sure they support passes in the Wallet app.
When you add a boarding pass, ticket, or other pass to the Wallet app on your iPhone, you automatically add it to the Wallet app on your paired Apple Watch.
Learn how to remove a pass or ticket from the Wallet app.
As mentioned above, if you can't add the reservation using the typical steps, then it would be best to contact the merchant or company that issued it to you. They may be able to send you a copy of the reservation with the needed information.
Wishing you well, take care.