Open an image
Now we gonna add the lens flare. Go to Filter > Render > Lens flare
Problem is that you add it to a grey layer and that you not can see where its apply in the picture. So cancel the action and select the Background layer. Now add and place the lens flare. If you happy with it click on OK. Now hit Ctrl or Cmd z to undo the lens flare. Select the 50% grey layer and hit Ctrl or CMD F to add to lens flare again but not on the 50% grey layer
Now we have the lens flare. Last thing we can do it to colorize it. Add a new layer. Select a warm foreground color and add a gradient. Set the blend mode to something like soft light.
(Alternative is to add a Gradient Map adjustment layer. )
You also can do it with a black layer and the screen Blending Mode.
Try it out and see what works best for your image. But be sure that you add the lens flare to its own layer.
picture from pixabay.com