If you need to redownload the update, try rebooting your phone. In order to avoid filling the storage with unused updates, the file is deleted once the update is done. Maybe rebooting your phone while reset it, but i’m not sure. If you need to install it via ADB, i can give you documentation and explain you but it’s not intuitive. Easier with a custom recovery like TWRP (->see the how-to). But firstly try to reboot your phone and see whether or not the update has been deleted.
Greetings !!
Edit: you possess a FP5 be aware of this issue (normally patch) before installing ! IT MIGHT HAPPEN !
Please read carefully this thread. The problem is normally patched.