Cannot untick [LR] locked tag next to post

Hi,
How do I make a grayed out ticked checkbox tickable/untickable again? The “[LR]” tag appears next to this Access property at the edit Post page. Whatever I do it does not help, I tried removing categories from this specific Post, I tried with Bulk Edit > Remove/Overwrite in Set up user groups section, nothing works. The greyed out group is stuck with this post forever. Please help.