The Lunar Lens is activated in the Location Entrance Window from the booster column on the right when you press the Use button.
Then you need to enter the location and zoom in on the scene by sliding your fingers away from each other on your mobile device or by using the mouse wheel on your PC. After that, the names of search items that can be found on the zoomed-in part of the screen will be highlighted in the search list.
If none of the items can be found in the zoomed-in area, you need to move it so that other items come into the field of view.