Trouble downloading newest version of IOS to my iPad 12.4 5th Generation

Any advise on how to proceed if I have already tried to download the newest software version to my iPad, but get the notice “can not update” “iPad will try again tonight” and therefore I plugged in my iPad & turned off iPad for the night and still can not update...

I am now trying to download my newest version of software by using my desktop by plugging in iPad to computer and looking in “Finder” for my iPad in “Locations,” but it is not showing up. ???? I did press on my iPad “Yes, Trust this Computer” when I plugged in iPad to computer and still can not find my iPad on computer. ??? Thank you for any and all help in this matter.