I know it shouldn't have vanished in the first place but it has. Any idea how to reinstall it without rooting or a hard reset? Cheers

This website has a link. Just go to the page on your phone and install it.

When I saw the title, I thought you had rooted the phone. I thought you could only uninstall updates not the app.
Definitely not there under manage apps? Have you rebooted? I wonder if there is a fault with the phone, and you may have to hard reset it.

Edit, I see there is a link to an apk in #2, but I still think you need to workout why it disappeared and if anything else is affected .