A game update restarted itself and I’m wondering if there’s a way to get the progress back

I was updating fortnite on my gaming laptop & my wifi is awful so it’s been 4 days of stop & start downloading this 38GB update at 0-1mbps. It was at 88% so i clicked continue install and went to shower while it ran, I’ve just come back and it’s now displaying 4%, the progress bar is completely reset. Does this mean that the 88% of downloaded material was never actually downloaded, or is it just a cosmetic glitch? does anyone know if there’s any way to solve this or am i going to have to do the update all over again?