Unable to disable lost mode

Hi shrikant49,

If you're trying to locate an AirTag, we recommend that you try the steps here: Find your keys, backpack, and more with AirTag - Apple Support

Next, we’d like to show you how to perform the recommended troubleshooting steps via the link above. Please click to open the link, then read through the steps in the section titled "Use Precision Finding to pinpoint the location of your item."

Find a nearby item

1) Open the Find My app, then tap the Items tab.

2) Choose your AirTag, then tap Find Nearby.1 Don't see Find Nearby? 

3) Follow the onscreen instructions and move around the space until your iPhone connects to your AirTag.

4) Your iPhone displays the distance and direction to your AirTag. Use that information to get closer to your AirTag until you find your lost item.

*When your AirTag is within Bluetooth range of your connected device, you can play a sound on your AirTag by tapping the Play Sound button . 

*If your iPhone says that more light is required, tap the Turn Flashlight On button .

5) Tap the Done button  when you're done. 

The reason why we are recommending the steps above is because they will show you how to locate your lost items.

If you're still experiencing the same issue, contact the community for more help.

Lastly, for your question regarding disabling Lost Mode, check out the article below in the section titled "Turn off Lost Mode on a device."

Mark a device as lost in Find My on Mac - Apple Support

When you find your lost iPhone, iPad, iPod touch, Apple Watch, or supported iPhone Wallet with MagSafe, turn off Lost Mode.

1) In the Find My app  on your Mac, click Devices.

2) In the Devices list, select the device you marked as lost, then click the Info button on the map.

3) Under Mark As Lost, click Pending or Activated.

4) Click Turn Off Mark As Lost, then click Turn Off to confirm.

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 My iPhone on iCloud.com. See Use Lost Mode in Find My iPhone in the iCloud User Guide.

Thanks for using the Apple Support Communities.

Cheers!