You'll probably need to reformat for instagram so that panels can fit in a square format.
A trick I do for reformatting is saving a file with only the panels visible and a transparent background as a png so that I can select and crop panels without having them all seperate files (shown below) It also means everything is on one layer
I use the polyline lasso tool to select and copy paste panels onto the vertical scroll format, so maybe you could do the same for instagram if it works for you
I myself, actually post my comic to instagram but in page format, and I have to widen the side of the image in order for it to fit on instagram. It's easier than reformatting (since I already do that for webtoon and I'M NOT DOING THAT AGAIN)