See the following from Find My iPhone: Lock and track your device using Lost Mode
You can turn off Lost Mode by entering the passcode on the device. For Apple Watch or an iOS device, you can also follow the steps below to change the contact information displayed on your lost device or to turn off Lost Mode.
Note: If your credit and debit cards for Apple Pay were suspended because you put your device in Lost Mode, when you turn off Lost Mode and sign back in to iCloud, you can resume using your cards.
- Sign in to Find My iPhone on this device with your Apple ID (the one you use with iCloud).
- In the Devices list, tap the device that’s in Lost Mode.
- Tap Actions, then tap Lost Mode .
- Change the contact information, or tap Turn Off Lost Mode.
You can also find instructions for turning on Lost Mode on a device on iCloud.com. Click the Help button ,then go to Find My iPhone > Use Lost Mode.