How to remove FaceTime lockdown mode on my iPhone?

Hello ValerieCG, LockDown Mode is an extreme security setting. To see if you have it engaged on your iPhone Go to Settings > Privacy & Security > Scroll all the way down to the bottom and see Security LockDown Mode. If it is on and you don't need the extra security the slide the Switch to Off.

Hi ValerieCG, Sounds like it was a Time Sensitive Notification that goes away after one hour. If that was the case in Settings > FaceTime > Notifications > Time Sensitive Notifications that can be turned off if you wish. Also you can change your "ALERT" setting too if you wish

ValerieCG, So confirm this is a FaceTime Notification you are trying to clear?