I've got some dust/dirt in my lens - Is there something I can do about it?

As the title says, I found a recurring smudge in my photos when I was editing this one. You can see the smudge in the middle of the photo.

At first I thought it was on the outside of the lens, so I cleaned it off. Still there.

I ran the "clean image sensor" program on the camera. Still there.

So I detached the lens from my camera body and when looking through it with the aperture wide open, I could see the particle that was causing the smudges.

I then took a photo of a white wall with the flash on at the widest aperture setting I could (f/36) which I will be posting at the bottom of this post body. There the middle smudge and a smaller smudge in the lower left can be seen.

Is there anything I can do to resolve this? I can see there are 3 screws at the camera side of the lens that I might be able to unscrew, but I have no idea what's inside or how complex it would be to pick apart. It wouldn't surprise me if I just introduced more dirt by opening it up.

The smudge is very visible at any aperture setting greater than about f/6.

I appreciate any feedback.

Photo of a white wall: