In Panovolo we have a built in blender for it when we detect that 360 pano is being stitched.
Manually you can try to cut a small vertical strip from left or right, mirror flip it horizontally and paste on the opposite side with blending. May work for some images, but not others because exposure compensation for left-right sides will not match perfectly.
PTGui is image stitching software for stitching photographs into a seamless 360-degree spherical or gigapixel panoramic image
ptgui.com
If you are talking about the JPEG files stitched by the drone, open them in a photo editor that supports 360° editing. I use Affinity Photo, which lets me touch up the zenith and nadir which sometimes need a little work. I also use Affinity Photo on my edited panoramas after Color Efex has processed the equirectangular files (because Color Efex doesn't understand 360° images), because then I do get a seam line that needs editing.
The tool I use for this is the inpainting brush, or sometimes the clone brush. Depends on the problem I'm trying to fix.
The only fully-loaded photo editor integrated across macOS, Windows and iPad, Affinity Photo is the first choice of millions of professionals around the world.