Improve 3D items scanned with a drone

Hello guys,
I am a newbie, so sorry for the silly question. Since I was little I wanted to create a 3D environment of my little city. I used to work with the Unreal Tournament Engine when I was 10 and started with my house.
Now I work with drones and they help me create 3D models from pictures I take around monuments. You can see an example here:
I was able to import this model into the Unreal Engine. The quality is quite good, but as you can see, once you get closer to the tower (you maybe have to wait a little bit before it shows the best quality) the windows are not very good. Also the door and the stairs are not in a good shape.

Before importing this kind of model, can I improve it somehow? Which software can I use?
Can I change the door and the windows with something from the Engine?
Which workflow do you suggest?

Sorry for the silly questions, I hope you can help me. It would be good to work with 3D models generated with softwares like Agisoft Metascan.


Ultimately, Agisoft should be able to get better quality scans to show those details, but if you’re using a drone you might not have a good enough camera on there to get a lot of detail.
To improve it otherwise, you’d need a tool that can do retopology (Blender is free and has those kinds of modeling tools)
What you would do is basically remodel on top of the 3D scan (clicking where you want vertices and choosing how they connect to create polygons) and then you would be able to model the details more easily.

These kind of models/monuments are better made in a 3d model programm with real-world measures (e.g. use a laser-meter for it,. and while youre at location take pics as basis for PBR materials).