Hi dbernath,
We understand you found a lost device and would like to start using it again. We're happy to offer some guidance.
To turn off lost mode go back to the iCloud website and go in to the Find My option. Select All Devices at the top of the page, then select the device you have in lost mode. Click on the Lost Mode option and select Stop Lost Mode.
Use Lost Mode in Find My iPhone on iCloud.com
Once lost mode has been disabled, the iPhone should prompt you to re-enter your login information for iCloud in Settings > your name at the top. After signing back in, you should be able to access your payment cards in the Wallet app again.
If you removed the cards from the device when you put it in lost mode, you can add them back to the Wallet app with these steps: Set up Apple Pay
Hope this helps. Cheers!