How to take phone off lost mode

When selecting Lost Mode when logged in to your iCloud account via webmail access using a browser:

• If you’re asked to enter a passcode, type the digits that will be required to unlock and use your device if it’s found. For greater security, use random numbers that aren’t associated with personal information (for example, don’t use the year you were born or your street address).Note: If your iOS device already has a passcode, you’re not asked to enter a passcode; the device locks using the existing passcode.
• If you’re asked to enter a phone number, you can enter a number where you can be reached. The number will appear along with your message (if you add one) on the device’s locked screen.
• If you’re asked to enter a message, you may want to indicate the device is lost or how to contact you, such as: “This iPhone is lost. If found, please call me.” The message will appear on the device’s locked screen.

To change the message or phone number shown on the lost device, or to turn off Lost Mode, click Lost Mode, then make your changes.

What is lost mode?

i believe he's talking about in icloud/find my iphone.