Reflections are a pain for sure, not being an expert here but it doesn't look to me like a reflection caused through your imaging train to the camera itself.
You don't say if your using a refractor or a reflector, that can make a difference as far as what is causing this problem.
I use a Newtonian and have problems where close lamp post light creeps in around my focuser where the draw tube goes into the body of the focuser.
Solution: I purchased some darkroom blackout material from a photographic shop (which you would use to line a dark room for processing images under red light), once my focuser is out at the focus position I wrap this material around the focusers tube which totally blocks out any light from entering this way.
If your using a Newtonian this could be not a reflection as such but more light leaking in at the mirror cell end (most cheaper Newtonians will have a fully open mirror cell where you can see the back of the mirror) - I had a huge problem with this and had to build a cover (which would still allow airflow for the cooling fans) to give me 100% light block at the bottom end.
My best advice to you is what I had to do:
In daylight, maybe in your living room, set up your scope, even on the floor, with the lens cap in place and the camera installed as though you were doing an imaging session. Take what would be the equivalent of a 3 min Dark. Look at the image when it comes and look for anything not perfectly dark (except for hot pixels) which might indicate light leaking in somewhere. If you see this anywhere on the image, get some kind of dark/black material and wrap it tight around your focuser tube for example, take the image again and see if the Dark is improved, do this all over your scope until you work out where light is leaking in. (Be careful with lens covers, sometimes they can allow 'some' light in through the plastic material itself, get a sheet of tin foil you would use for baking, wrap it over the end of your scope tube and secure with an elastic band or tape to ensure the lens cover is leaking no light whatsoever).
If the above trials prove that no light whatsoever is affecting a 3 min Dark frame then the reflection has to be external light in your environment, get your innards flocked, put up a screen if there is a light source close by, try the above tests while you scope is in it's imaging position outside.
Persevere and you will get there !
As to if it's possible to remove the problem in you image ?, the only thing that comes to mind is the new feature in 'Image Integration' called 'Larges Scale Pixel Rejection', whether it could take it out really is a question only Juan could answer but it's potentially possible based on what this new feature is aimed at, it's certainly a large scale artefact for sure.
Good Luck
Paul
