Open the photo you want to edit from the Lightroom library.
Click the “Develop” feature located in the upper right-hand corner of the Lightroom screen.
Open the “Graduated Filter” tool located in the “Develop” toolbar. You can also simply hit the “M” key.
Open different effects in the “Graduated Filter” tool. They will include effects such as brightness, saturation exposure, color and contrast. Since you are removing a sun flare from a photo, try eliminating the brightness first.
Use the cursor to highlight the area you want to edit. You can adjust the direction of the filter by moving the cursor near the filter pin in the center of the filter until the cursor turns into a rotating icon. Drag the filter in any direction to rotate it.
Adjust the settings of the effects by moving the scroll bar on the effects slider. Starting with brightness, try to eliminate the sun flare by sliding the brightness down to dark. Add other effects by clicking “show effects” in the upper right-hand corner of your panel. Try a host of effects and experiment with the effects slider on each one until you have satisfactorily reduced or removed the sun flare.
Add other graduated filters on top of the original, if desired. Hover over the original filter until the cursor turns into a cross-hair. Then repeat the process of editing with effects. Delete a graduated filter by clicking on the center filter pin and pressing the "Delete" key on your keyboard.