Remove my old Apple id
Turn off lost mode and remove old Apple ID.
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Read about how to use Lost Mode in Find Devices on iCloud.com
Use Lost Mode in Find Devices on iCloud.com - Apple Support
When you find your lost device, do either of the following to turn off Lost Mode:
- You can turn off Lost Mode by entering your passcode on the device.
- In Find Devices on iCloud.com, click All Devices, then select the device that’s in Lost Mode. Click Lost Mode, click Stop Lost Mode, then click Stop Lost Mode again.
Turn off Find My on your iPhone or other devices
Turn off Find My on your iPhone or other devices - Apple Support
How to turn off Find My iPhone on your iPhone
1. Open Settings.
2. Tap [your name] > Find My.
3. Tap Find My [Device], then tap to turn it off.
4. Enter your Apple ID password.
5. Tap Turn Off.
If you are asking about a secondhand device you have purchased, take it back to the person from whom you received it and get them to do the things in this support article or ask for a refund --> What to do before you sell, give away, or trade in your iPhone or iPad - Apple Support
Unless you have the account information that set the lock, or the original receipt from Apple, you cannot remove the lock; recycle the device. Read this article about how to remove Activation Lock --> How to remove Activation Lock - Apple Support