How to lock iPhone 6s Plus without iCloud or Find My set up
How To lock my device 6s plus Without iCloud Or Find my devices options not yet setup
I Just remember passcode
iPhone 6s Plus, iOS 15
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If the iPhone 6s is already lost (or stolen) and has not had Find My set up, you will want to change your Apple Account password, get the cellular phone plan transitioned to a phone you control, and check your trusted telephone numbers. Set up two-factor with an Apple device you already control, if two-factor authentication is not already enabled, too.
As for determining its location, there is no means for a user to do that, other than by having Find My already set up.
There is no means to enable Find My remotely.
If your iPhone or iPad was stolen - Apple Support