How to cut out the bridge?

Looks like the bridge is in daytime, but the black sky makes it look like night.  Might be easier to offer advice if we could see the original image.

Also, if you're wanting to put the sky back, then having the planet faded can also help to disguise the "trick".  

In Effects and Presets, search for Keylight.  A preset will come up that's got Keylight, CC Cleaner and Spill Suppressor already set.  That might help, but you maybe stuck masking out the bridge by hand.  (You could try rotobrush, I suppose).

It might also be worth trying out a few transfer modes.  Have an undoctored copy of the bridge underneath, then the planet then on top of that another bridge layer.  See if any transfer modes solves the problem for you.