Hello adamob,
Welcome to Apple Support Communities!
We understand that you deleted some of the passes from Wallet and would like to know how to retrieve them. We’d be happy to help.
Do you use iCloud? At the time the passes were deleted, in iCloud settings was Wallet switched on under "Apps using iCloud"? If so, the data from Wallet is stored separately from a backup so you would not be able to restore it. However, if Wallet in iCloud wasn't enabled and you have a backup (either in iCloud or stored on a computer) from a date when you still had the passes, you can potentially restore a the backup as an attempt to retrieve them.
You can retrieve the passes you deleted by adding them back from where you first added them from. Here’s some information on how to Add and manage passes in Wallet on iPhone.
Have a nice day!