If you marked it as lost, here is how to unlock it:
Mark a device as lost in Find My on Mac - Apple Support
Per Apple:
You can also turn off Lost Mode on iCloud.com or from your iPhone, iPad, iPod touch, or Apple Watch by entering the device’s passcode (the one you use to unlock your device). For a supported iPhone Wallet with MagSafe, you can turn off Lost Mode by attaching the wallet to your iPhone.
If you forget your device passcode, you can recover it using Find Devices on iCloud.com. See Use Lost Mode in Find Devices in the iCloud User Guide.